- Remove bunch of outdated TODOs
- Removed the stack for the back navigation for nested folders.
Instead, Back/Up will always just navigate to the parent mailbox.
- Two-pane UI controller no longer stores IDs by itself.
Now it always gets these from installed fragments.
- Added UIController.switchAccount(), which is the same as openAccount
except it's no-op if the account is already selected.
- Other small clean-ups.
Change-Id: Ie14bc4f4b6b2cf6afb69bc97967c25682d4c7c78
49de71e3d2