[Brightbox] Extract to provider module [GH-2647]

This moves all the Brightbox lib files to a `providers` subdirectory as a prototype of moving the repo files around.

A new gemspec exists which has built `fog-brightbox v0.0.1` - https://rubygems.org/gems/fog-brightbox

I have a branch of our CLI application (https://github.com/brightbox/brightbox-cli) using this which appears to be working.

`fog` now depends on `fog-brightbox` which brings all the functionality back.

The shindo tests have not been moved and (locally) pass.