new sample project demonstrating Datomic as a ‘graph database’

inspired from the Neo4j tutorial
the sample graph contains actors and movies as nodes and the ‘acts-in’ relationship as edges
the information about edges are stored in the transaction that recorded the edge
alternative version of movie graph sample
Merge pull request #47 from pellucidanalytics/topic/movie-graph-sample

new sample project demonstrating Datomic as a ‘graph database’