Use fuller format with committer info instead of medium format, as that
is more complete, and info for author and committer seems to fit in one
line each.
Fix one-line medium format so it truncates the subject at 50, instead of
at the fixed column 60, as that was not good to graph logs.
Remove `--all` from graph log aliases, to increase their flexibility.
We're then able to use it just for the current or for a branch passed
as parameter (as we already could with the other log aliases).
Copied from zimfw/git@63008c817e
507f5d58e0