Use controlled vocabulary identifiers as the solr values

[dannymandel]

Right now, the solr values for the controlled vocabulary appear to be the labels, e.g.:

http://localhost:8985/solr/isb_core_records/select?facet.field=hasMaterialCategory&facet=true&indent=true&q.op=OR&q=*%3A*&rows=0&useParams=

"hasMaterialCategory":["Natural Solid Material",2233939,"Organic material",1066279,"Rock",912855," rock",838805," sediment",838805,"Mixed soil",838805,"biogenicnonorganicmaterial",495052,"Material",462472,"Mineral",390797,"Biogenic non-organic material",346242,"mat:rock",309504,"mat:biogenicnonorganicmaterial",262200,"mat:anthropogenicmetal",251582,"ocmat:ceramicclay",105967,"Sediment",94084,"Not Provided",47173,"Soil",37153,"organicmaterial",35810,"Liquid water",25777,"anyanthropogenicmaterial",25632,"",9207,"Anthropogenic metal",4574,"Natural solid material",4574,"Gaseous material",1225,"Anthropogenic material",1168,"anthropogenicmetal",1060,"rock",953,"ocmat:organicanimalproduct",266,"Biogenic non organic material",195,"Particulate",124,"Non-aqueous liquid material",46,"Ice",8,"ocmat:plantmaterial",1]

Those should be converted to the identifier URIs. However, we should check that this is in fact possible for all records (see #312 for a possible hiccup).

[dannymandel]

For things to work properly, there is some UI work: isamplesorg/isamples_webui#186