Solve overlay problem and some refactoring

1. There was a problem with the editor. It appeared to be hovered by other annotation boxes. This was due to the osd-container which now has the minimal z-index of 0.

2. I tried to refactor the dupplicated code for the event listener of the editCanvas. Is this a good architectural approach?

3. I introduced some structures for keeping more than one selector. This is work in progress. 

Greets, chris