Create `list backups` functionality

[kiprasmel]

Task

• Create a function which would list backups

  • Local backups
  • Remote backups
  • Both
  • Decide which backups should be listed by default

• Implement an option to activate this function

  • think of a good name
  • handle in the script
  • update docs
    • raw
    • manual page

• Make it extendable for other commands (see Create restore from backup functionality #4 & Create delete backup functionality #5)

  • Make a single or multiple backups selectable (probably in interactive mode, something like git rebase -i)

Future

• Display which ones can be backed up (to where HEAD points to, checking if the changes could apply without conflicts (check by commits/refs/whatever-works, if possible, to avoid having to test every backup))

[kiprasmel]

It might be worth considering to stay as close to git stash as possible, and thus doing something very similar to git stash list would be enough and great. We can add sugar later.