Update the PollBot to gather data for a release health dashboard

[sylvestre]

Just like we have with the delivery dashboard, we would like to have a simple page with all the information about the quality of a release and a comparison with a the previous release(s?).

We would like to see (at least) the following items on:

• The crash rate. From http://arewestableyet.com/ or https://data-missioncontrol.dev.mozaws.net/ (see #198)
• number of tracked bugs. From Bugzilla (see #199)
• number of new and carry over regressions (see #200)
• performance with speedometer (see #201)
• number of uplifts accepted. Can easily retrieved in bugzilla (see #202)
• code coverage %. For now from codecov, later from our platform (see #203)
• number of defects found by Coverity and other static analyzers/linter. Outstanding defects & defect density (see #204)
• number of patches or bug landed in nightly (see #205)
• The uptake of the current release (we already have this information afaik)

Now, the trick is that we should also keep an history to understand how we are doing compare to the previous release at the same time (beginning of the cycle, end, etc). If needed, we could make progress to integrate the cycle span into product-details.
It means that we will have to store the data that we are retrieving.
-> See #206

The page(s) could be published on https://github.com/mozilla/moz-corsica/