Concepts tied to tagging process

[rob-metalinkage]

Current functionality is restricted to having tags defined in tagging process - you dont seem to be able to add labels in the admin form - and you cant have the same label in two different languages, or for two different concepts in different concept schemes. Basically the model is for one concept scheme - the tag space. Other things like having only one slot for skos:notation seem to be based on very specific use cases. I'll have a go at generalising it at https://github.com/rob-metalinkage/django-skosxl