Add default dialer checks to Telecom/Telephony

Check for the default dialer or the modify phone state permission
for various TelecomManager/TelephonyManager methods.

Make sure to check the user-selected default rather than the
hardcoded package name.

Exercise this code in TestDialerActivity.

Bug: 20304458
Change-Id: Ic04cd8f2ba98e1d54c39549ae89d3e11cd5cdafb