refactors editor menubar as preparation for undo/redo mechanism

Hello there!

I've started refactoring the menubar code towards a more structured approach, from which we will benefit in multiple ways. 

1. Code reuse by implementing a MenubarHelper, which creates and configures the Menubar Options in a centralised way.
2. Readability is improved when for option menu creation.
3. Both result in less repeating/dupicate code.

My idea now is to use the centralised MenubarHelper as first step, to transaction wise record all user interactions concerning scene graph modifications. Might be pretty naive but less complex than parsing, storing and applying diffs to the scene-graph json. 

Are you ok with these change? I would like to push this solution further. 

So long,
Dennis