Complex colorizer styles - full legends

This is a byproduct of working on a demo for @jonathanrobie

Morphology tagsets (as well as Relation tagsets) can now define styles on every attribute level - before we could only pick a category which was responsible for the colorscheming, e.g. the Part of Speech. Colors can now be combined, e.g. a verb 1st person can have a different appearance than a verb 2nd person.

It's the user's responsibility to make sure that the styles go well together - if e.g. two attributes define the `color` style, the second one will just override the first - no check is made to prevent this.

The Color Legends in the `helpPanel` reflect this change - as color styles can be given on any level, they now also serve another purpose: They are full legends and represent the complete tagsets.

Closes #362