Add ToS link to webapp

The user-visible substance of this MR is small: a tweak to the legalese at the bottom of the page. It also does a few things to make the lecture capture preferences app a little more modern:

• Add support for using Lookup credentials in development.
• Stop using demo.raven (stopping use of Raven Legacy at all is #8).
• Stop trying to call the Lookup API when running tests.

The preferences form now looks like the following:

The link in the small text at the bottom goes to https://help.uis.cam.ac.uk/service/teaching-and-learning/lecture-capture/staff/toolkit.

Closes #6