Neomodel-next

* add support for choices on string properites.

* updated documentation
* sphinx and rtd
* exception handling in cypher fix (tjakobsen)

* support for transactions
* new nodes class property (match API)
* support for neo4j 2
* no support for neo4j < 2
* deprecated category nodes
* deprecated index property

* server compatability check (Robin Edwards)
* 1.9 server fixes (Robin Edwards)
* upgrade to py2neo 1.6.1 (Panos Katseas)
* make __index__ inherited (Sebastian Ortiz)
* documentation improvements (Priit Laes)
* import RelationshipDefinition and RelationshipManager into main

* Display nice message for operations on deleted node (Robin Edwards)
* Re-enable lucene-querybuilder (Robin Edwards)
* Fix X-Stream header (Nigel Small)
* Enable custom indexes for StructuredNodes
* Support for relationship models or 'StructuredRels'
* Support filtering in the 'traverse' method (Robin Edwards)
* Store datetime objects as float for more accuracy (Robin Edwards)
* Setup NEOMODEL_FORCE_TIMEZONE env var to prevent storing of datetimes
without a timezone (Robin Edwards)
* Add NEOMODEL_CYPHER_DEBUG env var to log querys (Robin Edwards)
* Relative relationship classes in definitions (Panos Katseas)

* Add documentation on batch size (Robin Edwards)
* Fix default_value type generation for basic properties 53
* Add documentation on providing arguments to default functions (Robin Edwards)