Conda Store Authentication Mechanism

[costrouc]

Conda-store needs to have an authentication mechanism. The first step would be to make conda-store integrate with jupyterhub.

There would be a general authentication class similar to jupyterhub that will authenticate a given user and return user and groups that they are a member of.

Then a simple authorization mechanism would be added. Each namespace has read, write, list permissions.

A preliminary authorization mechanism would be read-only if username != namespace and namespace not in groups.

Would require token based authentication and oauth client authenticaiton.

Depends on #61.