[Feature Request] Generalize window controls

Hello, I would like to have generalized controls for different windows.

To achieve that there should be two changes:

1. Allow per-application header offset.

(Current state at the top, proposed at the bottom)

So this will allow to make groupy window to appear as application header.

2. Add controls for Groupy window to control current tab:

(Current state at the top, proposed at the bottom)

Not only this will appear more consistent than current solution, but also gives more comfortable controls, same as windows gives to the user.

Thank you.