REIVEW: [NX-518] Orient database manager

This PR addresses the following issues:

https://issues.sonatype.org/browse/NX-518
https://issues.sonatype.org/browse/NX-519
https://issues.sonatype.org/browse/NX-542
ah, i see now you've considered a memory impl...ok. either that or an alt. constructor would be fine for testing i think.