VE-1686: Loading animation

Loading animation for Venus guided by the video demo from our designers.

Oasis is largely unchanged although there is an improvement that the black overlay from the loading animation never appears at the same time as the focus widget and the toolbar never appears above a black overlay. Oasis improvements should be considered a positive side-effect and not the goal of this pull request.
Same check as in the other file, and same value (500) - so it convinces me more that it should be kept in one place - perhaps static field of the class.