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.
Feature specifications speak in present.

```cucumber
And the branch "old_feature" is deleted
```