Introduce a "Style" enum for compile-time checking of style names

Many places use hard-coded strings for component style names, and a number of which are fairly common ("font", "color", "horizontalAlignment"). It would reduce the possibility of misspelling of these style names if there were an enum for them so that the Java compiler would check spelling instead of finding out at runtime that the style name was misspelled.
This would involve adding methods to Component.StyleDictionary to deal with the enum as a key.