Allow users to delete git branches through the UI (BB-3336)

The syntax for deleting a git branch on a remote server is as follows:

#!bash

git remote -v
#copy the {branch-name} from the returned list
git push {repo_url} :{branch-name}

The essentially tells the remote git, match up my local branch (nothing on the left of the with the remote branch

effectively removing the remote branch. There should probably be a way to do this on the site as well.