Multiple database support and tests

Hello!

This pull request added integration with plugin https://github.com/biggora/caminte, and now plugin support
```
mysql, sqlite3, riak, postgres, couchdb, mongodb, redis, neo4j, firebird, rethinkdb, tingodb
```
and i add tests for database api.

The only problem I have not been able to test some of the responsibility for dealing with Bitcoins