#289 Scaffold Tree View: Hotkey for rotation not working when canvas focussed

[Sven Schrinner]

Steps to reproduce:

1. Open a scaffold tree view with any subset
2. Click inside the canvas
3. Press Ctrl+Left or Ctrl+Right: The tree is not rotating now

If the focus is switched, the hotkeys work again:

1. Click on one of the sidebar elements (e.g. choosing a sorting property) or switch to another view (using the view tab bar) and then back to the scaffold tree view
2. Press Ctrl+Left or Ctrl+Right: The tree is not rotating now