<UserEventLogging> Log app launches

b/26494415

1) Current Logger can capture taps from
- homescreen
- folder inside homescreen
- apps prediction
- all apps a-z
- tap from hotseat
2) Deprecate LauncherCallback methods that is no longer needed

Future CL.
3) Stats and Logger will be merged. Bundle used for Stats can be
replaced with LauncherLogProto
4) Logging anything else other than app launches

Change-Id: Id52eb615f66142017b5c490a220ce6654d325681