Drop OrientDB in favour of H2

[pavelhoral]

We want to replace OrientDB with H2 in Wren:IDM to make the build process and sample deployment simpler.

From its introduction into the platform was OrientDB meant only as a demo database. OrientDB is not a simple project and it makes the build process unnecessarily complex, is quite bulky and introduces additional issues (#58).

I am proposing to switch to H2 for several reasons:

• It is well established database engine for testing purposes.
• It is pure Java and has a small footprint.
• H2 has it's own console UI application if we need it.

What I am not sure of:

• Don't know how well H2 plays with OSGi... but AFAIK that should not be an issue.

This issue is more about dropping OrientDB rather than about introducing H2. The final end goal might be to go for embedded Wren:DS, but that is not ready.

[pavelhoral]

Resolved via #92 .