Update documentation on managing consent with survey consent frames

[becky-gilbert]

Fixes #372

This PR adds a section to the 'Coding Consent' documentation page about handling responses that contain survey-consent frames. This documentation update is to go along with changes we've recently made to the EFP and lookit-api (https://github.com/lookit/lookit-api/pull/1330) to make sure that responses with survey-consent frames become available to researchers, and to flag them in the Consent Manager view.

This PR also:

• updates old screenshots so that they reflect the site's current style/layout
• makes minor edits to the text in the existing "Overview" and "Managing Consent Ruling" sections

Here are a series of screenshots showing the rendered Coding Consent documentation page with the changes made in this PR:

Edit: I've noticed and fixed a few typos since taking the screenshots above:

• Remove "the" from "In general, all studies on CHS should use the video recordings for consent. "
• Add the missing word "should" to "You set up your study in one of the following ways:"
• Fix spelling error (Mangaer -> Manager) in "We do not pull the consent questions/answers out of the response and present them in the Consent Mangaer,..."