RPM Support

Before adding support of modular content the format was:

{"applicability": 
     {"rpm": ["unit_id1", "unit_id2"], 
      "erratum": ["unit_id3",]}, 
"consumers": ["your_consumer_id1", "your_consumer_id2"]}

Now "modulemd" content type will be added:

{ "applicability" : 
     { "rpm" : [ "94978496-8bda-43f7-bad3-70aed533cf83", "a78438e6-453f-4ad5-8071-02f6c18b35a4" ], 
       "erratum" : ["12345678-8bda-43f7-bad3-70aed533cf65" ],
       "modulemd": ["87654321--453f-4ad5-8071-02f6c18bdead"] },
  "consumers": ["con1", "con2"]
}