Separate settings modules to make testing easier
Add more utils functions

* new get_cassandra_connections function to return list of all
cassandra conncetions defined in DATABASES setting
* get_cassandra_connection now accepts alias and name parameters
* get_cql_models now can return models for given keyspace
Update DatabaseIntrospection

cql_models in DatabaseIntrospection now returns all cql models for
given keyspace
Present new test application: multiapp

This application helps with testing multiple cassandra aliases
Refactor test runner

Now test runner is able to run django tests with different settings
modules.
Move syncing code to sync_cassandra command

Also update .travis.yml to run only on Cassandra 2.0.
Update docs