git prune-branches

@kevgo please review

+ Changed a couple git helpers to take in parameters instead of operating on the current branch
+ Set the default branch on the remote repo to main (needed as the git prune-branches feature specs were deleting the master branch (since its not main) and you cannot delete the HEAD branch on the remote repo.
This reads ambiguously. Where is the old_feature branch deleted from? My repo? The remote repo? The coworker repo?

```cucumber
Then the following branches exist
  | repo     | branches          |
  | mine     | main              |
  | remote   | main              |
  | coworker | main, old_feature |
```