Placement of the editing canvas controls

[miselico]

Currently, the buttons to control the canvas are placed in the editing box and disappear on certain editing actions.

I suggest moving them on top of the canvas itself.

[JohannesLipp]

Thanks for the hint! This might require major changes as the graph editor / canvas is a dedicated component based on mxGraph. I will discuss possible solutions with @husaynali on Thursday.

[alihussainiam]

Implement drawing elements/buttons on the canvas.