Basic getTest / addResult Cassandra backend implementation

[gwicke]

Progress so far: #13
Calling the CassandraBackend constructor will

1. Retrieve all test identifiers (prefix and title) from Cassandra
2. Retrieve latest test scores corresponding to retrieved test prefixes and titles
3. Order retrieved tests by placing them in a priority queue

Will be done soon (Sebastian and Krishnan):
- Dummy data  + verification that the logic so far works (Somewhat done)
- Queue retry/fail logic

Dummy data progress: https://gist.github.com/swong15/9061167
  we can also check this in, maybe in a cql/testdata subdir -- Gabriel
Scores are randomly generated. Commit hash is arbitrary for now. Should suffice to test current logic. There are more sane ways to do this rather than calling a large number of inserts. This is just a quick and dirty way of verifying correctness for now.

Data (including non-english characters) seems to load fine from server after inserts are done from cqlsh.

cqlsh doesn’t take non-english input well.
Queries break on text like:
insert into tests (prefix, title) values ('itwiki', 'Museo_di_fisica_dell'Università_di_Napoli_Federico_II');
This looks more like a quoting issue to me. You need to escape the embedded ‘ with another quote: insert into tests (prefix, title) values ('itwiki', 'Museo_di_fisica_dell’'Università_di_Napoli_Federico_II');

Who: Krishnan, Collin, Junjun, Pranav, Sebastian