Add cmake option PARSER_ONLY to build only the parser, as the name says.

This removes the dependencies on kholidays and ki18n, when all that is wanted is a parser.

Impact on the API: setRegion/region/interval/nextInterval is not available when this option is set. setLocation/setTimeZoneId (and getters) are available but have no effect, maybe I should remove them too.

All the methods for evaluation have been moved to evaluator.cpp. An alternative to splitting the implementation of internal classes like this would be to move code into an Evaluator class, but input welcome before such a big change.