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.
I envisioned this for just stale and outdated feature branches. 

The empty feature branches is a side effect of the implementation (they count as merged). 
Why would someone push up a branch without a commit?

Hmm, abandoned feature branches are interesting. I think these need to be looked at on a case by case basis. At least for the initial release of this I'd prefer to leave it out and we can revisit it specifically later.