Merge branch 'bi-queries'

Use the 'test' task for testing. Fixes #190

Ingraph compiler written in Xtend based en EMF and supported by VIATRA.

At this version, the ingraph-compiler have its metamodel defined in
the Eclipse Modeling Framework (EMF), using Xcore.

Compilation of openCypher queries are supported by VIATRA transformations.

The majority of the compiler is written in Xtend.

introduce IngraphElement

add IngraphElement superclass for IngraphVertex and IngraphEdge