Allow to select a reporting period in Repository charts

Description

Currently Repository > Charts reports on a given ref and 2000 latest commits, hardcoded. I found it very useful to see my commit count trend in the first month I was using gitlab but I am no longer able to do it, as "Commits per day of month" shows both January and February commits, summed up.

Proposal

Allow for selecting a period from/to next to the ref. Repository model has both after and before arguments, there already is a frontend calendar widget, so I believe this should come down to just a couple lines of code.

Alternatively, and even better, also have another repository bar chart with up to 30 days of commit counts per day, similarly to "Commits per day of month", obeying the selected period.