Improve super key overlay

Made the following improvements to the keyboard shortcut overlay:

• Made overlay width dynamically adapt to length of shortcut texts (previously, some shortcut texts would clip out)
• Streamlined shortcut texts (#66)
• Prevented super key and window switching overlays from appearing on login screen.
  • My approach somewhat goes against the suggestions in #62. I just prevent the overlay from rendering when orblogin window is detected. #62 suggests disabling super key events entirely.