GenericHighlighter: prioritize color settings

It would be nice if you would handle highlighting in a more generic way (as additional highlight definitions can be downloaded) :

• if a highlight definition has a defined key (dsString, dsKeyword, dsDataType,...) completely ignore the color definition of the provided xml and always use the defined color of the current scheme
• if a highlight definition has not a defined key but provides a color use this
• if a highlight definition has not a defined key and does not provide a color on its own use some default (dsNormal?)

Note: it would be even more cool to have the ability to define own keys for a custom scheme. E.g. you know that some highlight definition uses 'dsSpecialFunction' you could define a color/font definition inside your custom scheme explicitly for this key which would be used.