GRBL 1.1f update

exams are over, grades are good and I finally have time to work on my projects again.

this update should work with grbl 1.1f.
Since I can't access my machine currently, I didn't have the chance to test this on my machine.
When I tested it with a bare Arduino board, it worked well, so I don't expect any major flaws.

Updates include:
-support for GRBL 1.1f (no backwards compatibilty)
-ability to save modified files (#3)
-file dialogs remember their location (#11)