Allow deleting multiple branches

[haideralsh]

Problem description

Currently the only way to delete branches is either individually via the command palette Delete Branch... or individually using the Locations tab in the side bar. I usually like to delete a bunch of branches after doing a fetch --prune, but currently there is no way to delete more than one branch at a time in Sublime Merge.

Preferred solution

Allow using Shift or Ctrl / Cmd to select multiple branches in the Locations tab to delete multiple branches.

Alternatives

• Allow selecting multiple items in the command palette.
• Offer a command to delete fully merged local branches that don't have a remote counterpart.

[srbs]

duplicate of #677.. however, I think we should keep this issue as it has a much better description