Improve parsing of TaggerTypes in tagging functors

Make sure that requesting undefined taggers results in an immediate error, instead of just resulting in some default (useless!) values in an NTuple, by using parse instead of TaggerTypeToType. The latter maps undefined taggers to 'unknown', which will subsequently not be found, and not found results in default values... The former instead throws an exception if the name is not known.

requires LHCb!5379 (merged) (which fixes a bug in parse)