DEV: patchbot: update: name the touched commits in the storage messages

DEV: patchbot: update: name the touched commits in the storage messages

Every save used to be committed as a bare "update 3.5", which makes the
storage history useless to navigate. The subject now names the branch
and the first commit whose review was touched, followed by "+ N more"
when several, and the body lists all of them one per line:

    update 3.5: 6a7b27a0 + 2 more

    6a7b27a0
    d13aaf05
    b12dd0b5

This is what to grep for when hand-editing the storage repository, for
example to locate the change to revert or rebase. A commit touched by
several directives of the same save (state plus notes) is only listed
once.