Scale fonts more carefully
This commit is a total overhaul of font scaling. The available space in a label is calculated, as is the needed space for N lines of the configure font. If necessary, the font is scaled, as a float, to fit. The linespacing is set to 1.2 times the font size, which looks ok.
The font is never scaled up, contrary to the previous code.
The necessity of review and dealing with long lines remains.