Implement Ctrl shortcuts for common tasks

[SimonBuxx]

• [x] Ctrl-C and Ctrl-V when new copy system is implemented
• [x] Ctrl-S when saving is implemented
• [x] Ctrl-O when loading is implemented
• [x] Ctrl-1 to Ctrl-9 to set gate input count
• [x] Ctrl-Arrow Keys to set component direction
• [x] Ctrl-Return to start/stop simulation

[SimonBuxx]

https://doc.qt.io/qt-6/qshortcut.html

[SimonBuxx]

Shortcuts are implemented (partly with no executed code)