Rendering settings unification

This PR deals with several issues to make Insight's rendering settings panel look and behave like Web's rendering settings panel. 
Test:
* Check that the arrangement of the UI elements is the same like in Web (order/name of the buttons, etc.)
  (also compare to [Rendering Settings-Preview Pane Round 3](https://docs.google.com/document/d/1aI-od_kCpymL6TX5ydxGbNnVC_LcEjVroL1YsSGD3QE/edit) )
* Check that the various actions still work and have the same behaviour in Insight and Web: Undo/redo, copy/paste, viewing other user's rendering settings, and so on.
* Check that the ROI count label shows the correct number of ROIs

There is still one flaw: Copy, paste and save actions are not working properly for the renderings settings panel shown in the full image viewer. But they might be hidden anyway, when shown in the image viewer (to be discussed). I'm going to deal with this in a separate PR, as this one is already quite large. 

Also not part of this PR (dealt with in a follow-up PR): Zoom functionality in preview