Use the DataONE SolrClient to perform searches

[ThomasThelen]

The DataONE python library has a class for performing searches against the DataONE SOLR service (we query the SOLR service when locating and obtaining information about datasets during lookup&registration).

Right now we're using requests directly with DataONE and manually parsing the response. The library has methods for doing things like

1. Counting objects that match a query (we do this by hand in a few places)
2. Searching
3. Obtaining information about objects

I'm currently marking this with low priority since this code already works and there are currently higher priorities.