adding neo4j-embedded db back to store participant graph in an experiment.

should also consider running a full neo4j rest server and using https://github.com/versae/neo4j-rest-client, as
neo4j-embedded looks unmaintained
adding lazy graph module, still need to figure out how to properly manage the embedded graph db lifecycle:

1. use a context manager to automatically shutdown the graph db after each request, inefficient as initializing the
GraphDatabase takes a fair amount of time
2. install a shutdown hook on wsgi to shut down the graph db on server halt
3. always invoke vcweb.core.graph.shutdown() at the end of an experiment
4. move to a standalone neo4j rest server (managed via supervisord?)
5. store the graph in the RDBMS for simplicity

--HG--
extra : amend_source : 2fa82a0fe338966cab8be7b108ccb0e1b951fe94
cannot use default kwarg, need to refactor *data_values usage
refactoring GroupCluster/GroupRelationship/Group creation to prepare for large group networked experiments.

probably going to go with a straightforward RDBMS approach to minimize external dependencies on neo4j. using
neo4j-embedded involves a fair amount of complexity surrounding how to properly initialize the graph datastore, model
the data, and manage its lifecycle (clean shutdown, etc.)
more refactoring / cleanup
improvements to tests, starting to favor creation of actual DataValue entities in lieu of creating DefaultValues when
asking a DataValueMixin class for a data value
ignoring .coverage data
refactoring tests, splitting into modules. fabfiles are next to hopefully be able to use fab in drone.io

--HG--
rename : vcweb/core/tests.py => vcweb/core/tests/test_models.py
fixing sphinx docs and refactoring fabfile and settings
more test refactoring
test invocation fixes
refactoring
adding dashboard view test and default value coverage
adding participant view test
moving requirements.txt up to top level

--HG--
rename : vcweb/requirements.txt => requirements.txt
pushing import down to avoid early jpype dependency
adding roledefs and initial postgres config

TODO: replace by loading settings_staging.py instead
ignoring htmlcov

--HG--
extra : rebase_source : b45e700381b5fafa4a200cbe304945407af2ff89
extra : amend_source : 84daf67b86e1090c5b4e4e4403e5f97f61864e0f
minor settings refactoring
settings.py cleanup and trying to set the postgres database explicitly for drone.io