Make sure plan descriptions of entity producers / start items contain a producerType entry

o Also adds list of identifiers to these descriptions
o Renames StartItem.name to producerType
Document how Cypher compares values by equality and for ordering
Merge pull request #1698 from boggle/2.0-cypher-comparison

Document how Cypher compares values by equality and for ordering
fixing rest api such that nodes or relationships are indexed properly, where before dummy nodes were indexed in their place
changed rest api for create_or_fail semantics: if you request indexing a node under key foo and value bar, and that node or another node is already indexed under foo/ bar, then an error is returned
Merge pull request #1705 from jakewins/restapicreateorfail

fixing rest api such that nodes or relationships are indexed properly, w...