Refactor Managers

* Moves managers to SoftLayer.managers
* Moves manager tests to SoftLayer.tests.managers
* Adds missing manager imports so that all managers are exposed as SoftLayer.ManagerClass
* Adds missing hardware manager to the docs
* Adds Firewall Manager Test
* Renames capital manager modules to lowercase
* Moves manager exceptions to SoftLayer.exceptions
* Adds a couple missing module doc blocks

Should resolve #99