AnnotationTool improvements and fixes

Feedback from Korbi:

Bugs

• Frame seeking sometimes laggy
  • Basically, the 🌀 does not disappear ...
• Shortcuts for new events seem not to be working (Ubuntu 22.04)
• Event template labels sometimes interpreted not as polygon but as point
• Application title is unknown (on Ubuntu) or python (on macOS)
• Global save state sometimes erroneously marked as unsaved, e.g. after changing to a new file
• Lag when changing points (adding, moving, deleting …)
• Error message scroll area below metadata editor and label list is taking up too much space

Improvements

• Choose better colors for spatial labels
• Double-clicking on event start/end time should go to corresponding frame