Updated API to saerch on availability prefLabels

[qjhart]

Searches now look like

 http http://localhost/api/search type==expert availability=='Collaborative projects' Authorization:"Bearer $jwt"

and normal aggregations liist like:

  "aggregations": {
    "availability": {
      "collaborative projects": 2,
      "community partnerships": 1,
      "industry projects": 1,
      "media enquiries": 1
    },
    "type": {
      "expert": 4
    },
    "status": {}
  },

[qjhart]

@UcDust the only confusion I see is that the keyword is lower case, but that doesn't match the actual URLs. I'm not sure what's best. Otherwise it's in your side now.