Added typeface initialization to CustomLookAndFeel, and implemented
getTypefaceForFont().

Fonts can now be created using a more centralized method, by calling the
Font(String("Typeface Name"), fontHeight, Font::style) constructor.  Names for
the typefaces ("Default Light", "Paragraph") should be regarded as tentative.

There's also simpler code to do the same thing that should be uncommented after
the 2.0 update (it uses HashMap, which is not currently in our library code,
even though it's in the 1.53 docs.)