Feature: automation, handle external commands, closes #22

- clicking on current track's name will show track statistics

## Automating

- μlogger may accept commands from other applications for starting or stopping its operations. To make it work you must explicitly enable this functionality in app settings ("Allow external commands" switch). 

- Commands are sent as `broadcasts` with following `intent` parameters:

  - target package: `net.fabiszewski.ulogger`

  - target class: `net.fabiszewski.ulogger.ExternalCommandReceiver`

  - action: `net.fabiszewski.ulogger.intent.action.COMMAND`

  - extra: `"command": [command name]`, where command name is one of: `"start logger"`, `"stop logger"`, `"start upload"`, for starting and stopping position logging and starting track data upload to server (in case live tracking is off)

- Third party examples:

  - Automate (LlamaLab) – Send broadcast block with `Package`, `Receiver Class` and `Action` fields as above and `Extras` field eg. `{"command": "start logger"}

  - Tasker (joaomgcd) – System → Send intent. Fields `Action`, `Package`, `Class` as above and `Extra` field eg. `command:start logger`

- command line: `am broadcast -a net.fabiszewski.ulogger.intent.action.COMMAND -e "command" "start logger" net.fabiszewski.ulogger net.fabiszewski.ulogger.ExternalCommandReceiver`

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                <category android:name="android.intent.category.DEFAULT" />

            </intent-filter>

        </receiver>

        <receiver

            android:name=".ExternalCommandReceiver"

            android:exported="true"

            tools:ignore="ExportedReceiver">

            <intent-filter>

                <action android:name="net.fabiszewski.ulogger.intent.action.COMMAND" />

            </intent-filter>

        </receiver>

    </application>

</manifest>

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/*

 * Copyright (c) 2019 Bartek Fabiszewski

 * http://www.fabiszewski.net

 *

 * This file is part of μlogger-android.

 * Licensed under GPL, either version 3, or any later.

 * See <http://www.gnu.org/licenses/>

 */

package net.fabiszewski.ulogger;

import android.content.BroadcastReceiver;

import android.content.Context;

import android.content.Intent;

import android.content.SharedPreferences;

import androidx.core.content.ContextCompat;

import androidx.preference.PreferenceManager;

public class ExternalCommandReceiver extends BroadcastReceiver {

    private static final String START_LOGGER = "start logger";

    private static final String STOP_LOGGER = "stop logger";

    private static final String START_UPLOAD = "start upload";

    @Override

    public void onReceive(Context context, Intent intent) {

        SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(context);

        boolean allowExternal = prefs.getBoolean(SettingsActivity.KEY_ALLOW_EXTERNAL, false);

        if (!allowExternal) {

            return;

        }

        if (intent != null) {

            String command = intent.getStringExtra("command");

            switch (command) {

                case START_LOGGER:

                    startLoggerService(context);

                    break;

                case STOP_LOGGER:

                    stopLogger(context);

                    break;

                case START_UPLOAD:

                    uploadData(context);

                    break;

            }

        }

    }

    /**

     * Start logger service

     * @param context Context

     */

    private void startLoggerService(Context context) {

        DbAccess db = DbAccess.getInstance();

        db.open(context);

        if (db.getTrackName() == null) {

            db.newAutoTrack();

        }

        db.close();

        Intent intent = new Intent(context, LoggerService.class);

        ContextCompat.startForegroundService(context, intent);

    }

    /**

     * Stop logger service

     * @param context Context

     */

    private void stopLogger(Context context) {

        Intent intent = new Intent(context, LoggerService.class);

        context.stopService(intent);

    }

    /**

     * Start logger service

     * @param context Context

     */

    private void uploadData(Context context) {

        DbAccess db = DbAccess.getInstance();

        db.open(context);

        if (db.needsSync()) {

            Intent intent = new Intent(context, WebSyncService.class);

            context.startService(intent);

        }

        db.close();

    }

}

    public static final String KEY_USE_GPS = "prefUseGps";

    public static final String KEY_USE_NET = "prefUseNet";

    public static final String KEY_LOGGER_RUNNING = "prefLoggerRunning";

    public static final String KEY_ALLOW_EXTERNAL = "prefAllowExternal";

    @Override

    protected void onCreate(Bundle savedInstanceState) {

    <string name="pref_autostart_title">Auto start</string>

    <string name="pref_autostart_summary">Application will start on system boot</string>

    <string name="pref_autostart_default" translatable="false">false</string>

    <string name="pref_external_title">Allow external commands</string>

    <string name="pref_external_summary">Allow receiving commands from other applications to facilitate automation and tasks scheduling.</string>

    <string name="pref_external_default" translatable="false">false</string>

    <string name="pref_provider_title">Location provider</string>

    <string name="pref_provider_summary">Location may be supplied by gps provider, by network or by both. Both providers will give best results, but use more battery.</string>

    <string name="pref_units_title">Units</string>