UI improvement on Notifications page

[Jakob Hermann Preusker]

Nearly the same as in issue #27. Here a possible solution:

As you can see, the Refresh button is placed like in #63, and the Mark all as read button like the New issue button on issues page.

[Aalok Singh]

I'm thinking of moving the refresh and 'mark all as read' button to bottom of the page like a commandbar. This way we won't have to add a refresh button to HeaderPanel on the MainPage,