move video compression into camera class

Moved into record_video()

Put missing self arg in record_video()
allow scancam moves to return while in action

Added wait_for_completion arg to scancam_base.move_stages() and
xthetaz_scancam.move() so that we can allow video capture during the
second z-axis move through the depth of the culture.
add scancam_base.in_action() function