Featrue Reqeust: extend TreeView

[rwaffen]

@tuxmea please put your feature request from the slack in here... thx :)

I want to have the possibility to compare two hiera data structures from different environments.
Something like a complete diff of the whole data tree.

Workflow:

• Select env
• Klick show tree
• Have a "diff with..." selector button, that allows you to select another environment.
  The result is shown as an overlay. Similar to "Show lookup results"