Bugfixes

Pressed Ctrl + Enter by mistake.

Other stuff included:
- Only one instance allowed
- Unused menu items removed
- Small gab between buttons on titleBar added [subject to change]
- Start up position changed to be slightly lower [subject to change]
- Default overlay number is now 1
- Import .txt now has the txt-filter as default
- Open preset (.csv) now as the csv-filter as default
        - How the the loading is changed slightly to include the parameter of preferred filter