Reverts most changes to MainActivity and uses handleSpecialIntent
instead. handleSpecialIntent now defers installer prompt to
InstallerService by starting it again.
SpecialIntent has been modified to accommodate extra data needed to
handle these callbacks.
Fixes "tap to install" notification not launching an activity. Install
notifications moved to InstallerService so that we only show them for
apps that need intervention (and lets us preserve our install session).
All installs go to the installer, allowing for downloads to jump
straight into installation if possible (auto updates or showing prompt
on A9 and earlier). If a prompt is needed, the notification is still
shown.
Additional utility function checks if app is in the foreground. Used to
ensure that we do not launch a prompt that cannot be launched.
Miscellaneous comments have been added and improved.
