Embed the app restrictions fragment in the dual-pane settings.

Change the limited user creation flow to show the usual message before
actually adding the user. Might need to customize the message for limited
users.

Removed the old activity wrapper and moved the logic to UserSettings.

Removed the finish button.

Bug: 8566751
Change-Id: Ie9e1a03736c41758b0bb6e79d004ad662a5af7f4