Feature/store infection probability

[matteopariset]

Store and show the evolution of user's probability of being infected

[codeclimate[bot]]

Code Climate has analyzed commit e658d23a and detected 0 issues on this pull request.

The test coverage on the diff in this pull request is 82.0% (80% is the threshold).

This pull request will bring the total coverage in the repository to 80.2% (0.0% change).

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