[GORA-650] [WIP] Add initial ArangoDB datastore

[dinuka-perera]

Work in progress ArangoDB datastore implementation.

[djkevincr]

@dinuka-perera Thank you for your hard work during the GSoC period. PR looks very good. Please update the PR with offline review we had, and fix rest of the test cases related to datastore queries. I m going to keep PR for a while for let others to review. Good Luck with your final evaluation.

[SemanticBeeng]

@dinuka-perera please advise on plans for this - thanks

[kamaci]

Thanks @dinuka-perera!

Please review my comments and resolve the conflict.

[djkevincr]

This work is redundant and superseded by work here. [1] Hence closing the ticket. [1] https://github.com/apache/gora/pull/291