Add an opt-out and opt-in experience

The current implementation of the module is to inform the user that cookies are being used, on the assumption that they will not use the site if they disagree. However, on first visit, cookies will be set and javascripts the can potentially track the user will run.

Two other methods of handling cookies are opt-in and opt-out:

• Opt-in will not track the user at all until they have given consent. In this case we will only set the cookies that do not track the user, and any first-party and third-party tracking should not run.
• Opt-out will track the user, but will respect their decision to not be tracked and stop any tracking if they later opt-out. In this case, cookies will have to be deleted when they choose to opt-out and scripts that track the user should no longer run.

I suggest that this is implemented in module configuration as a new pane - Implementation, that will offer 3 alternatives:

- Inform the user that cookies are being used on the site
- Use cookies by default, let the user opt out from cookies
- Don't track the user unless they give consent (this last option may be GDPR compliant).

A second pane will then offer to exclude certain javascripts from running when users have opted out or before they have opted out.

A third pane will offer a way to whitelist cookies that can still be set even for users that opted out or haven't opted in, assuming these cookies will not identify the user, or be used to track their browsing. Such cookies may be the PHP session cookie and the cookie used to store the user's cookie compliance choice.