uistyle: Add more type-safety to UiStyle, and clean up a bit

Migrate all UiStyle enums to be enum classes. Enforce explicit types
instead of quint32 in most places using them, and handle MessageLabel
in a more obvious fashion. A bunch of bit-wise operators had to be
added to avoid lots of boilerplate when dealing with the enums.

FormatList now holds the formats in a struct rather than as plain enum
(or quint32) values. This will be needed for extended color support;
as the format type cannot hold the hard-coded extended color values,
the colors will be stored explicitly in the list and applied as
appropriate.

Also, in the quest to modernize the codebase, FormatList is now a
std::vector rather than a QList.