Added a new extension for oauth2 providers that integrates with flask.

Modified the existing scopes argument for django provider so that it now will
accept a function as well as a list object. This is done so that scopes can be dynamically
set.
Small modification so that the dynamnic scopes now will pass the requests object in django.
Updated the documentation for dynamic scopes.
Fixed a small error with the flask extension.
Removed the use of the flask g object from the extension, the properties can now be pulled from the OAuth2ProviderDecorator
Merge pull request #148 from flippmoke/master

Flask OAuth2 Provider and Dynamic Scopes