Add a settings page.

[tylervz]

Add a settings page for signed in users. It should use the route /settings,

Allow users to revoke oauth access from this page.
Later, we may want to allow them to specify default print settings (color, collate, double-sided, etc).

I have already partially implemented this enhancement. My work can be found on the branch settings.

[tylervz]

See revoke_cloudprint in api.py.