Add back a SYNC_SETTINGS screen

Revive the old Accounts&Sync screen as a dialog with the auto-sync
checkbox and a list of accounts. This will be launched when Apps
request a SYNC_SETTINGS page for controlling account and master sync.

Auto-sync data checkbox will also continue to exist in Data Usage.

Minor fixes to account list and account update monitoring.

Bug: 6614013
Bug: 6622995
Bug: 6610247
Change-Id: I35c0919a29c6bc7e5edf64f2734a3ef4f5ae5e7a