Corrected font metrics computation.

In Qt4 the actual font size depends on the device that will actually
paint the font. To avoid to explicitly ask the painter to compute
the font size we can use QFontMetrics::QFontMetrics(font, 0) to
always obtain the correct screen metric (behavior similar to the Qt3
default). All istances of QFontMetrics have now been so modified.
Additional font metrics corrections.

Corrected the font metrics handling in several components, also regarding the pin numbers position. Added some more comments in the code.
Updated the deprecated Qt3 support parts.

Changed the deprecated Qt3 support functions with the equivalent Qt4 code.
Merge pull request #98 from in3otd/fontsize

Font metrics