Added a method to ToastUtils that will show the old authentication alert if the XML-RPC error contains 403 or 503. Currently works in Posts/Pages and Comments list refresh. TODO: Needs to be added in other places where we use XML-RPC calls such as Media.

I haven't tested this on self-hosted sites yet.
Update wpcom password for blogs available in the app
Add callback to RefreshPost|Page Task that catches XML-RPC auth errors
Add the wpcom Authorization Header if needed
Remove extra call to updatedWPComCredentials, as it occurs within the WordPressDB.saveBlog() method.
Remove showToastOrAuthAlert call in onPostExecute, since the prompt is now handled by the listener.
Fixed loading blog setting for self-hosted sites. Was missing blog id extra.
Revert "Add the wpcom Authorization Header if needed"

This reverts commit 919402468870cc9dc8765014d5d5e0e4ba050867.
Added support for auth prompt in Media.
Show a correct error message when 2FA authentication is enabled on the account. Make sure to call get/me to retrieve a correct OAuth token when the login is done. Changed the incorrect username/password message.
Make sure the login dialog shows when refreshing Notifications List.
Make sure the activity is still active
Fix an issue where Stats doesn't show the sign-in dialog - instead it fails silently.
Use utility method VolleyUtils.volleyErrorToJSON
Fix an issue where showToastOrAuthAlert() is not checking if error 503 is due to a login limit
Remove unused imports
Merge pull request #902 from wordpress-mobile/issue/899-xmlrpc-auth-failure

XML-RPC auth failure