Reformatted Settings dialog so that longer paths can fit as well

Path Entry boxes are made 3 columns wide (instead on 1), three buttons
just above Save/Cancel are placed in these columns, with some x-padding,
and this the paths are extended. They fit my paths nicely.
Even better would be to make contents rescale when window is resized, but
that requires some intricate .grid layout manager manipulations...

Release LeMMA 0.9 under the GPLv3