integrate portal webview to the default app

Based on the UX review feedback, we plan to implement portal webview
function inside the carrier default app instead of reusing the existing
portal app. This will give us more flexibility and control, also will
improve UX flow by getting rid of the some unwanted dialogues.

new added CaptivePortalLoginActivity is a copy paste from
com.android.captiveportallogin/CaptivePortalLoginActivity combined
with logic from deleted LaunchCaptivePortalActivity.
All webview UI was inherited from com.android.captiveportal

Test: Manual
Bug: 36002256
Merged-in: I2627d5a43039ce433006c058bb4f2c1a39113e59
Change-Id: If422fa12c5f24d9b9e2c9380b3edf94df74bb85f