Add an ignore_tags configuration option to ignore annotations in make

[Ninjani]

Problem

Some annotations don't need to be present in generated knowledge base. Maybe they're addressed already, or specific to a short-term task.

Solution

An ignore_tags configuration option that gooseberry make uses to ignore annotations with given tags.

Alternatives

Possibly also a complementary keep_tags option that only generates annotations with given tags. Either option can be used but not both.