Refactor UserEventLogging, Add predictedRank, replace Bundle with Proto

b/26494415
- Removed bundle object that became redundant now that we have LauncherEvent proto
- Combined Stats and UserEventLogger as they are effectively doing same thing
- Removed parent field inside Target
- added predictedRank target inside Target

b/27967359
- make com.android.launcher3.action.LAUNCH broadcast explicit
Later CL: finish packageName/intent/componentHash/predictedRank fields

Change-Id: I441fb46c834f73e58a4d2324e8da7971e8713ec8