MetricConfigurations cache on MezuroConfiguration's show #46.

Signed-off-by:Beatriz Rezener <beatrizrezener@gmail.com>
Signed-off-by:João Gabriel <joaogabrieldebrittoesilva@gmail.com>
Improving the solution #46
Merge pull request #150 from beatrizrezener/issue46

MetricConfigurations cache on MezuroConfiguration's show #46.
Acceptance tests for ReadingGroup destroying
Merge pull request #151 from beatrizrezener/issue39

Acceptance tests for ReadingGroup destroying