Add support multi-purpose amenity

[Nekzuris]

There is no consensus on how to map multi-purpose amenity, but you should add support for semi-colon value separator because currently it’s impossible to find an amenity=restaurant;cafe like this.
https://wiki.openstreetmap.org/wiki/Key:shop#Multi-purpose_shops

Also in general semi-colon value separator should be better supported, contact:phone often use it too.
It's very useful sometimes but has very low usage because mappers know that consumer apps have very poor support for it in general tags.

[plepe]

That's quite a lot of work, as it requires to change each category (where this is relevant). In 61ba758 I changed some categories.

I also added support for phone, website and email (and 'contact:'-prefixes) in b3d1aa5