Adding app specific screen so that third party apps and package
installer can directly intent there to direct users to change the
setting. Also added automater tests.
Test: adb shell am instrument -w -e class \
'com.android.settings.applications.ExternalSourcesSettingsTest' \
'com.android.settings.tests/android.support.test.runner.AndroidJUnitRunner'
Bug: 33792674
Bug: 35487166
Change-Id: I5a481ee7032979df94a9e267ea74aa90da6a0906
Added a preference link to manage external sources in the app info
screen just like other special access permissions.
Test: Manually checked that the link appears on apps once their app op
is set to allow or deny.
Also, added some basic robolectric unit tests:
make -j32 RunSettingsRoboTests
Bug: 35481942
Change-Id: If687778b7a64fb7d278508b78d06272253a98e3e
Added a settings fragment to manage external sources. It lists all
applications that have either requested REQUEST_INSTALL_PACKAGES or have
their app op changed from default.
Test: Will include in follow-up CL. Tracked in b/33792674
Bug: 31002700
Change-Id: Ibd2a1922be214b62aec4eefa45f7b9691256b205
