Removed ServerUnavailableError exception.
Updated requirements.
Added calls to inject_into_urllib3().
Updated requirements.
Added a note about scheme adjustments for OAuth requests to server.
Using the same URL scheme for OAuth requests as specified in config.
Revert "Using the same URL scheme for OAuth requests as specified in config."

This reverts commit aab65d6563eb3a3b0e897d5e322f9ce83c027c57.
Cleanup.