Toolbar shortcut tooltips

[osn07]

Keyboard shortcuts in the tooltips are not working great with Mac (shortcuts are stored as "Ctrl+..." not "Cmd+...").

Also, structure of shortcut tooltips should be changed --> assigned with rest of tooltip, not in KeyboardShortcutManager's register_tooltip(). Then, when a shortcut is updated, the UI is reinstantiated to update live.

Relevant Files:

shortcuts.py
base_instrument.py
instruments.py