Need class for getting consistent font sizes across platforms

[nikreiman]

Annoyingly enough, calling Juce::Label::setFont() with a given size in points results in radically different sizes on Windows and Mac (with Windows being much larger, usually). Linux fonts are probably also yet a different size.

Need to measure the difference between sizes and provide a class that gives the correct size for a given platform based on the requested size. Only a few point sizes are probably necessary to determine (ie, everything from 8-18).