Enable custom user analytics tagging

[cbunicef]

As an ADMIN I would like the option to use an analytics platform of my choice, rather than Google Analytics Universal Analytics via djga as currently offered.

As an ADMIN I would like the option to not use Google Tag manager for custom analytics tagging, so user data doesn't need to go to Google.

As an ADMIN I need to be able to add custom analytics code to test its function, without replacing current analytics function.

As an ADMIN I would like to be able to customize analytics code on a per-page, inheritance-possible basis. (I believe there is another issue for this)

As an ADMIN I would like to be able to specify whether a site-wide tag applies to Admin Panel or public site or both.

A suggestion for configuration in Admin Panel:

Site-wide tagging -

In Site Settings, a section for "Tagging", with content blocks where users can add multiple tags
These tags are included in the site header

Per-Page tagging -

In Page Settings, a section for "Tagging", with content blocks where users can add multiple tags with inheritance options
These tags end up at the top of the Page content

To consider:

• how do we allow for flexibility to incorporate different tagging solutions, eg JS, pixel, server side
• how do we sanitize inputs
• possibly each tagging solution format needs to be specified in the codebase as a content block type? As Google Analytics via djga is today
• what happens to the current scheme of Local vs Global tags?