Feature/ocsadv 23

These changes address the GUI issues brought up in OCSADV-23, disabling the unbounded position angle option for MOS imaging and custom mask FPU observations (and FPU = None).

Also, this fixes a bug with respect to the parallactic angle controls appearing when they shouldn't.
(See REL-2089: http://jira.gemini.edu:8080/browse/REL-2089)
The problem here is that I'm creating the ParallacticAngleControls when the PositionAnglePanel is constructed (if the instrument type supports the parallactic angle feature, and at construction time, we don't have an instance of the instrument itself). I suppose it would be possible to maybe move this into an init method and do it at initialization rather than construction, but this would necessitate a fair number of changes (the card panel would also have to be built at initialization time rather than construction time, for example).

Do you think this is something we should do?