[WIP] Add tests everywhere

[r0mainK]

#58

[r0mainK]

@vmarkovtsev tests failing because the version of sourced-ml package seems to be too outdated, compared to the git repo. We might wanna release a new one ? Else we can install it using git

[r0mainK]

Wrote tests for as much stuff as possible. Currently bags, graph, main and cassandra_utils files are covered fully or almost. I want to add some for query, but regarding hash functions idk if Travis can handle all the GPU stuff. I also added a parameter to the Cassandra cluster because we often get connection timeouts with resetdb, from the logs i think it solves it for the most part.

[r0mainK]

@vmarkovtsev let's merge this after #61 so I can modify/add tests for new ml and apollo features

[r0mainK]

Added Konst's changes from PR #66 so tests would not fail, will update the rest of the code asap

[vmarkovtsev]

#66 was merged

[r0mainK]

Great, will rebase and take care of conflicts asap. Ill also update the doc regarding the preprocess command