Fix tooltip to display as white and not transparent

I finally found some time to fix this annoying visual bug.

After thinking the problem was that robotmain.cpp was not creating a Button and tried various fixes, I came up with this simple fix, which I think is correct.

The second commit tweaks the margin around the text a little to have the letters leaning down (such as "g") with a little more margin.

TIA, cheers,
OdyX