Group MetaData fields

Currently the metadata is flat, e.g. not hierarchical. Some metadata fields however are strongly coupled and even more so, now we have introduced multiple discovery items.

Introducing the concept of groups looks intimidating, however we can solve this without much refactoring solely on the client. Add an optional group attribute to an existing property and filter out metadata that belongs to a group. A group item always has a multiplicity of > 1 and the cardinality of an item can be determined by parsing the :{nbr}: from the attribute name. For each unique group we render + add and - remove functionality.

This is only visual and under the hood (and the server) the data structure will not change. Estimated effort is ~2 days.