Create `delete backup` functionality

[kiprasmel]

Task

• Create a function which delete backups
  • Figure out how we want to display current backups so that we can
    • select one or multiple of them
  • One of them
  • Multiple
  • All
  • Make it work with remote backups (git push origin :branch-name)

[kiprasmel]

Imitate git stash drop|clear. Though we'd instead need to delete the branch remotely and locally, so git branch -d would be used instead.

It'd be great to be able to delete branches in bulk.