When receiving data from the LTI launch, or service call, only update
the user record when we know something has changed. This prevents the
creation of many \core\event\user_updated events.
This isn't required and generates excess events. The only thing update
does, other than update the user fields, is to update the picture, but
in this case, that's unset in membership-based auths anyway, so it's
entirely safe to remove this.
Three modes are initially introduced here, for use by dependent code:
1. Automatic - where accounts will be automatically created for users
2. Prompt new or existing - where the user can choose to use an existing
account or have a new account created for them.
3. Prompt existing only - where users must link an existing account.
This change also adds linked logins, for use with provisioning.
Jake Dallimore