ADD Cred per contributor for each period.

[amrro]

Description

As per this Motivation, you can view each cred/contributor/period percentage.

Test Plan

Using yarn start and manually viewing it.

[amrro]

These numbers are buzzing me.
SourceCred has 0.1472043202747623 creds. But it got formatted to 0 cred. But % Cred is showing otherwise.

I think this will vanish in large data set, but it probably is going to happen more with contributors that have less than 0.5 creds, especially in week's beginning when the gap is not the big.

[amrro]

Closes #3163