We need to handle pfsDesign files that have fewer than 2394 science fibres allocated

FPS assumes that pfsDesign files assign positions to exactly 2394 science fibres.  We need to be able to handle files that differ in at least two ways:

• Some fibres may not be allocated (e.g. when only SM1 is installed at Subaru, or probably during open use observing)
• Some of the fibres have a targetType of TargetType.ENGINEERING, and don't correspond to any cobra

FPS needs to map fiberId to cobraId, and this will probably automatically drop the engineering fibres.

The missing science fibres should be assigned to the centre of an unused cobra, which could be done either by FPS or by the plate design software. When possible, of course, they should be assigned to sky objects rather than plate centres which suggests that the best place might be plate design.