Some ActivityThread/ActivityManager cleanup.

- Move PackageInfo out of ActivityThread, renaming to LoadedApk.
- Rename some of the other PacakgeInfo inner classes to better
  represent what they are.
- Rename HistoryRecord to ActivityRecord.
- Introduce AppGlobals, to eventually let ActivityThread become
  package scoped.

Change-Id: Ib714c54ceb3cdbb525dce3db9505f31042e88cf0