Filter by tag

[valitas]

Make it so that different related buildings (like all buildings in the same chain) can be given a "tag" by the user, which then can then be used to view only those buildings. E.g. I want to type #ccwest in the filter, and see only the Cor Caroli West handweapons chain.

This is already implemented in Filter (it will recognise a #tag and will ask for the tag property of the Building instances it filters. Just depends on #38, or some other way to give the user a UI to set those tags on buildings.