The picker's options are data: CctvControls computes the cameras in view
and the closing note for those left out, keeps a focused picker's list and
prepends a camera activated under it, and publishes the options, disabled
state and selection. CctvPicker renders them keyed by camera id and
applies the selection once the options are in place; it updates only when
the controls publish, as the old picker did on layer notifications. A
picker about to be disabled no longer counts as focused.
This completes the CCTV panel: everything it shows is rendered from the
gev-cctv store.