Innovation day - Initial share project workflow

[sra405]

Endpoint and administrate dashboard to allow projects to be shared and moderated.

• is_live is used as well as user_id being null for public access to projects
• share endpoint copies the project and nulls the user_id and sets is_live to false
• administrate dashboard show "internal" projects (i.e. projects where user_id is null)
• shared projects are visible in the dashboard and is_live can be set to true to make them public

Current share endpoint is a tweaked version of the remix endpoint except user_id isn't set and locale is hardcoded to en

Associated frontend changes - RaspberryPiFoundation/editor-ui#702