Use real fragments for incoming/outgoing/exchange settings

* From account settings, switch to incoming/outgoing/eas fragments
* Show "Next" button in actionbar (may be dup'd in single-pane view)
* Common base class for in/out/eas fragments
* Depends on PreferenceActivity.startPreferenceFragment(), new API
* If the user clicks an account header while editing server settings,
  present a dialog before discarding the changes that haven't been
  checked yet.
* Confirm working (if a bit ungainly in appearance) on phone screen

Change-Id: I03591b9a8ffd11fe26fc6f58a5698740e61d0090
1 file changed