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
diff --git a/res/values/strings.xml b/res/values/strings.xml
index 0c6f341..7f120d7 100644
--- a/res/values/strings.xml
+++ b/res/values/strings.xml
@@ -587,6 +587,11 @@
 
     <!-- "Setup could not finish" dialog action button -->
     <string name="account_setup_failed_dlg_edit_details_action">Edit details</string>
+
+    <!-- On AccountSettingsXL, dialog text if you try to exit in/out/eas fragment (server settings)
+         without checking/saving [CHAR LIMIT=none]-->
+    <string name="account_settings_exit_server_settings">Discard unsaved changes?</string>
+
     <!-- On Settings screen, section heading -->
     <string name="account_settings_title_fmt">General settings</string>
     <!-- On Settings screen, setting option name -->