ev-window: stop using EV_CHROME, since it's no longer needed

For what I understand from the git log, at the point this whole concept was introduced, the UI had many elements that could be dynamically show and hide. That is no longer the case, and most things (everything but the sidebar and the find toolbar, the second of which is not kept track through the "chrome") are always showed. Or have some simple logic around it. Therefore, this whole feature is not needed, and can be replaced by some otherwise very simple logic in specific places.

Depends !637 (merged)