Make cookie restrict mode configurable, support google opt out cookie.

This PR adds 2 options to the backend:

*  Respect Cookie Restrict Mode

Currently when cookie restrict mode is enabled in Magento and the User did not accept the cookies the tracking code will not render. This creates problems when using a FPC, unless you punch another hole for the tracking. This new option enables users to still render the tracking code even if the user did not accept the store cookies and use option 2 instead:

* Support Google Opt Out Cookie

As an alternative this options provides support for using a Google Opt Out cookie. Requires placing a link to the opt out function in your relevant CMS pages (privacy policy etc). Snippet is provided in the comment section.

Disclaimer: We are running this patch in production, it might need some further adjustments when using multiple analytics accounts though.