Categorization of providers

[chseifert]

From a UI point of view it would be helpful if we had a categorisation/tagging of providers.

For example, I can then choose to get

• scholarly content
• cultural content
• educational content, or
• any two of them

The reasoning behind this is that we can't expect users to know about KIM.collect for instance.

Required changes (in my opinion):

• partner registration needs to include tags, tag set has to be predefined (e.g. partners have to state the categories of their content, e.g. "cultural")
• getRegisteredPartners should also return the tags
• the search request must include search for tags (in source selection)