Add FITS fields to actorkeys dictionaries.

Now that INSTRM-236 is done, populate the actorkeys dictionaries for all the actors whose status will go into a FITS file. For SPS, at least ics_enuActor, ics_xcuActor.

Yes I should write real documentation, but will sketch that out here for now.

Most FITS cards will come directly from actorkeys annotations. Each individual field in a keyword has grown a FITS option, which must be a pair of names: one a proper 8-character SUBARU PFS card name and the other a longer, more descriptive one. As an example, from the meb dictionary:

Key('flow',
       Float(name='Flow_meter', units='Hz',
             help='Flow meter reading',
             FITS=('W_MCFLOW', 'MCS_COOLANT_FLOW'))),

would automatically generate a FITS card like:

W_MCFLOW= 1.2 / [Hz] Flow meter reading

Note that both units and help are picked up. Beware that comments will be truncated at the usual 80 characters, so you need to keep the help field concise.

The biggest constraint is on the short name, which must start with W_ and must be no longer than 8 characters. So far I have tried to indicate the subsystem in the first character or two ("MC" for the MCS camera), and possibly a type in the last character ("T" for temperature, say). Doesn't leave much.

The longer name should be a little more descriptive. Grab a prefix like MCS, and make sensible names using {} separated words. Not _too long – the name eats into the comment space. We had hoped to use these as HIERARCH cards, but I think we are giving up on that.

The INSTRM-236 routines can create a long-to-short name mapping HDU, and I think will: 6 characters is simply too short to give meaningful names.

The ics_actorkeys dictionaries then become the reference location for most FITS cards. The camera actors will insert their own cards via a different mechanism, for values we probably do not want as MHS keywords (the many internal voltages, say). Maybe we do.