Font metrics 

as explained in #91 and #87 we need to know the actual font used for the components text to have its size computed correctly, as this is not usually the font requested. I put together a quick fix, basically using the current schematic tab to determine the font metrics; note that I had to move the `Module::registerModules()` call at startup to be sure to have a schematics tab created first, since some component are rotated just after being registered (!). 
I think there should be a cleaner solution to this, so this PR is just to show where things need to be fixed, hoping someone can come up with something better.