Implement General Preferences

- Removed the place holder setting
- Added "auto-advance" setting, which has "newer",
  "older" (original behavior, default) and "message list"
- Strings were copied from Gmail

This CL has preference change only (i.e. the setting isn't used yet).
The actual implementation will come later.

Change-Id: I9f90a723c67e066fdc536a73490101817a127933
1 file changed