Registration of new elastica driver and its extension

[chives]

Basic elastica driver (fsi-open/datasource#59) will be using only plain https://github.com/ruflin/Elastica. Here in datasource-bundle we can extend it to use all features of https://github.com/FriendsOfSymfony/FOSElasticaBundle (finders, transformers, etc.)

[norberttech]

Dependencies between bundles smells to me.

[chives]

This would be only optional but not required dependency

[norberttech]

Anyway its still bad idea.

[chives]

Registration of https://github.com/fsi-open/datasource-elastica-driver will require integration tests with fixture app and vagrant. Transformation from \Elastica\ResultSet to entities and their indexation should also be done in this bundle (instead of fsi-open/datasource-elastica-driver#11)