Show Loading Indicator

[hediet]

Testing #7422

When I click on a commit with many changed files, it takes a while until the multi file diff editor opens and there is no immediate UI reaction, so at first I thought it wouldn't do anything.

I suggest to show a loading indicator.
Also the multi diff editor should support lazy loading (there is a feature request assigned to me somewhere)

[alexr00]

We should show a loading spinner to the right of the commit title if you click on the commit title, and to the left of the commit sha if you click on the commit sha:

[osortega]

Verified running locally