Major under-the-hood updates.

- Begin work on APIv2
  - change the way permissions work
  - add optional worldReadable flag
  - ability to set a content description
  - fix a bug with ExtensionData parceling
- Add private read API (DO NOT USE)
- Pass extra to extension settings activities

Change-Id: Ifcd3adb50457d50e745d05eb3f261ad15b48740f