Loading spinner should have tooltip and may be repositioned

Added a Google account in the accounts section of gnome-control-center

Started calendar. Calendar start loading and shows a spinner in the top left corner.

## Problem
a) The spinner is in a different location than in the AppCenter (top right corner there). There should be more consistency across elementary apps.
b) There should be a tooltip with detailed information what calendar is working on (for example if you have multiple online calendars - which one it is currently fetching)