Core: association metadata index (#389, #338).

The association metadata index basically works. Both, indexing and query. Update is pending.

Core is not yet functional.

Furthermore, in order to determine an object's type the new storage layer doesn't rely on "Instantiation" associations anymore. Instead a "type_uri" property is stored for every object (= Neo4j Node). (The "Instantiation" associations remain to exist).
This provides the basis for solving #338 (An Association's "Instantiation" Association has no type assignment).

Furthermore in Parent POM: we explicitely use an older Surefire version (2.12.4) in order to avoid an exception logging problem introduced in Surefire 2.13

See ticket 389.
See ticket 338.