Resets the initial state of a HORUS session.
The operator close_horus resets the initial state of a HORUS session. In particular all image objects in the database will be deleted and the image size reset to 512 x 512. If the user intents to execute the operator init_horus shortly, using close_horus becomes unnecessary as the procedure will be triggered by init_horus anyway.
The operator close_horus always returns the value TRUE.