Easy use of coordinates as discussed in #10 and minor fixes

Fixes:
- Higher contrast between currently executing line and background
- No more overrides of warning, error, info gutter symbols by executed

New:
- Hold shift and click on a part of the map to choose the coordinate that should be pasted. It will paste the coordinates as a JSON ready to be used in `this.move()`. 

To-Be-Done:
- Change cursor logo. Currently it is using the standard crosshair but it would be cooler to have a custom flag-sprite.