create custom exception/error handling mechanism

As a follow up from #177 

Would like to spice up the frontend test only by adding one more level in the routes/contents created in the FixtureLoader to see both ancestor and parent suggestions.
its unique per BestMatcherRepresentation i would say. chain is a term not used elsewhere in this class so its confusing.

i know why you call this group, but maybe identifier would help making clear it has to be unique.