Add git notes in the commit metadata

[AdrienLemaire]

We're using git notes in our company, and it would be very appreciable to be able to read them in barkeep in addition to reading them in "git log" (especially for new-comers who didn't set their git config properly).

Hope that it piques your interest, thanks in advance !

[cespare]

Interesting idea. We'd be glad to look at pull requests if anyone wants to implement this.