Caching retrieveClansSummaries responses

[matheuscscp]

Problem: retrieveClansSummaries fetches a lot of data for many clans in most use cases (clan rankings). On a load test we detected that database CPU usage reaches 100% with a small load (compared to the load we expect for the launch of our next game).

Solution: Cache clans summaries individually, because players are used to rankings with information a little bit delayed.

[coveralls]

Coverage increased (+0.4%) to 62.118% when pulling fd2e3fa on matheuscscp:feature/clans-summaries-cache into 80586f6 on topfreegames:master.

[codingllama]

I've done a first pass, let me know your thoughts. Bear in mind that this is the first time I've looked at this code, so there's a lot of context that I'm missing.

[codingllama]

Please add a description to the PR explaining what the problem is and how we're attempting to solve it.

[matheuscscp]

Please add a description to the PR explaining what the problem is and how we're attempting to solve it.

Done!

[codingllama]

Thanks for the changes and for the added PR description, @matheuscscp.

[codingllama]

LGTM (Looks Good To Me).

Please wait for Camila's approval, but otherwise feel free to merge. 👍

[cscatolini]

Feel free to merge if you think this is ready or once you've incorporated the latest suggestions by Alan.