knowledge: REST API addition

* Implements a first prototype of Rest API to deprecate
  old kb export. (addresses #2570)

Signed-off-by: Leonardo Rossi <leonardo.r@cern.ch>
I added a static method!
Also extend the match_types (now 'sw' is supported).
Can I deprecated the `get_kbr_items()` and `get_kbr_values()` method and invite to use the new `query_kb_mappings()`? :)