Improved loading state UI for stream details

[TehNut]

Currently, neither the cover image or creator image/name are gated behind the loading flag so they will both display a broken image before the stream data is resolved. The shimmering class was also never applied, which seems like it should have been judging by the page css. This puts them both behind the same conditional logic as other elements on the page.

I have never touched Angular before this, so I tried to match what was already there.

The new loading state looks like this:

The removal from themes/_stream-pages.scss is because it was affecting the color of the profile image background on dark theme. I didn't look too far into it, but it seems to always return the first value in the if above.