Add CDNManager, which currently provides an account list
Implements basis of CDN and origin pull support

Supported commands thus far:
* sl cdn list
* sl cdn detail
* sl cdn load
* sl cdn purge
* sl cdn origin-list
* sl cdn origin-add
* sl cdn origin-remove
Resolve rebase conflicts and #pep8probz
CDN Initial tests and fixture
Some pep changes and logics

Add maximum constants
Minor CLI help corrections
Complete CDN tests for 100% coverage (alleged to be passing)
Fix string type checking in Python 3.x
Docblocks, copy-paste doc fix, and OCD placation (basically kidding)
Merge pull request #289 from briancline/cdn

Implements CDN Manager and CLI support (#47)