Rename git 'pick-commit' to 'pick-commits'
Rename git 'pick-commit' to 'pick-commits'

The alias lets you pick multiple commits (whether they're allowed by
the calling command or not) so this gives it a more accurate name.

Also allow specifying the branch name to pick commits from,
defaulting to the current bracnh.

kbd/setup,kbd/setup,kbd/setup,kbd/setup,kbd/setup