Corrected SFTP support with modifed sftp transporter (issue: #142)

[edmooney]

This is to correct issue #142 django-storages sftp initialize function did not allow passing parameters, this modified transporter accounts for this.

[wimleers]

Thank you! :) :+1:

There are a lot of "debugging" commits in there. It'd be great if you could clean those up.

I understand if you don't have time for that. But in that case, it'll be some time until I can work on manually merging this I'm afraid.

[squamous]

Would love to have this fix in @wimleers @edmooney I'm more than happy to contribute to get this fork merged