Improve SolrProxy to not depend on EmbeddedSolrServer

[dsmiley]

Even if you don't want to use SolrProxy with an EmbeddedSolrServer, SolrProxy has that dependency; which in turn triggers a ton of Solr stuff. If SolrProxy.initialize_embedded(home,core) were implemented in a static inner class, then EmbeddedSolrServer wouldn't be required if you didn't want it.

[mubaldino]

Will look at this tweak in Nov. Maybe even under the guise of the Solr 7.1 look.

-m