Is called to allow moderator to give reason for topic move.

• Must be called with a topic specified ($topic global variable)
• Uses the MoveTopic template and main sub template.
• If the member is the topic starter requires the move_own permission, otherwise the move_any permission.
• If post moderation is enabled, the topic must be approved, or the user must have permission to approve topics in order to move it
• Is accessed via ?action=movetopic.