Support OAuth2 with personal access token for command line access

[cliu587]

Our OAuth2 workflow is redirect based, which only works if the user has a working browser environment. For users who wish to programmatically access Coursera APIs on an environment without a browser (e.g an EC2 instance), they currently need to copy over the pickled access token from their local laptop.

Ideally we can support the generation of access tokens similar to GitHub (see https://help.github.com/articles/creating-an-access-token-for-command-line-use/), and short of that, provide some doc/support for the copying of pickled access token pattern.

[IshwarBhat]

@cliu587 I just got started working with courseraresearchexports, and we use an EC2 instance too. Any progress on this issue?