Settings: fix bug where user cannot uninstall launchers

This will fix the case where 3rd party launchers have both buttons
 "Force Stop" and "Uninstall" disabled.

Now, allow 3rd party launchers to be uninstalled or disabled. And
 allow system launchers to be disabled. Except when we detect only 1
installed launcher(system or app), then do not allow uninstallation or
disabling of the app to make sure there is always a launcher available.

Change-Id: I8cde7fd508fa16928e68e093141f7007ac6cd700
Signed-off-by: Roman Birg <romanbirg@gmail.com>