Ship CommonsExtension with some default schema templates

[lokal-profil]

This comes out of #86 and some related discussions on how you can reduce the need for wikitext in the Commons extension.

The idea is that you could ship the CommonsExtension with a handful of schema templates supporting some of the core cases (Artwork/Photograph/...) where the templates on Commons are already fully SDC enabled so that the wikitext could be fully static.

[lokal-profil]

I'll try to rephrase this issue later but this was one of the things discussed with e.g. @trnstlntk at Wikimania.