REST: Enable token auth support

REST: Enable token auth support

Token authentication is generally viewed as a more secure option for API
authentication than storing a username and password.

Django REST Framework gives us a TokenAuthentication class and an authtoken
app that we can use to generate random tokens and authenticate to API
endpoints. Enable this support and add some tests to validate correct
behavior.

Signed-off-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Signed-off-by: Stephen Finucane <stephen@that.guru>