Anton/editor tabs for studio

Adds tabs for modules editors in studio via TabsEditingDescriptor. Support for HTMLModule and Videoalpha has been introduced. All is backward compatible. 

Aim: Add tab support for videoalpha and html modules.

Features
1. Every tab has it's own html and css and js inside html.
2. Every tab has to care about callback on tabswitching: interface provided.
3. Every tab has to care on it's own save function: interface provided
4. Decoupling of editors looks good.

Things that are not perfect:
1. Name of Settings tab is hardcoded, due to special behavior (Showing Settings as tab should hide "Editor", "Settings" line)
2. Tabs names are hardcoded in callbacks. This is better as it was because there is clean way to sync tabs and save.  May be things can be improved there.
3. Tabs line look not very nice, when settings are hidden, @frrrances can you please look at it.

@cahrens and @rocha please review.