Refactor shortcut management, part 2

[farmaazon]

The PR for previous task #13002 improved many things, but still there are remaining issues:

1. We define shortcuts separately from actions: I think they should be in the same place - shortcut defined in action should also allow creating handler for it.
2. We still attach handlers to window or document which makes some actions possible even if graph is not visible. Also, see this TODO
3. @somebody1234 proposed making a Command Search, which does not work with our current approach - it's hard to judge when action should be available and when not. Perhaps we should reconsider making our own focus/constraints.