Add a simple version of a "get_count" utility method that return the length of a call to get_all_list_data.  Added corresponding tests.  Update OAuth2Bearer class to raise an exception if the token passed in is empty, not just None.  Added a new test for that case.  Import RequestContext in base canvas_sdk init file for easier access.
Merge pull request #18 from Harvard-University-iCommons/feature/get_count

Add a simple version of a "get_count" utility method that return the len...