New features:
- Add background color setting also to edit menu
- Add separators to the file menu
- Fix GitHub Issue #23: Setting for edge thickness
- Update icon (not sure if better)
Bug Fixes:
- Fix GitHub Issue #29: Errors when exporting to PNG not handled
- Fix GitHub Issue #22: Floating nodes cannot be deleted
- Automatically add file extension if filename manually entered
Other:
- Code refactorings