This commit is the initial work to move `Pull.flare` to storage.
This column has crashed the DB in only 1 occasion in the past.

Notice that Pull doesn't have `commit` (because multiple commits refer to the same pull).
To deal with that I changed the writing of data to have 2 paths: one with commit, and one
without the commit. So pulls data will be written in the repo level (in storage).

codecov/engineering-team#70