last used serial port pre-selection logic change, based on if it is autodetected to be present or not

Closes #41
Closes #51

Paint travel moves with a different colour

French translation fix

Fix inverted Y coordinates in normals

Only adds the STL filename to the listbox, not the whole path.

Conflicts:
	plater.py

Conflicts:
	plater.py

Crudely arranges the added STLs on the bed. Does not attempt to optimise for
space or anything, just arranges them in a rough grid.