change cdu  URL to URI   to use custom schema like 'memory://'
add AutoCloseable
- decouple database-implementations
- add  memory:// scheme for test-dbs
- make neo4j-rest dependency optional
- add optional neo4j-memory db-dependency
Merge pull request #39 from tbaum/master

decouple db-implementations add memory:// scheme
add Unique-Indexing
Merge pull request #42 from tbaum/unique-node

add Unique-Indexing