Add {{icc declareCurrentPfsDesign}} command

We need to declare to iic and hence to gen2 which pfsDesign has been chosen. The minimum the iic command needs to do is:

• find and load a given pfsDesign.
• allocate visit0
• generate a iic.pfsDesign=designId,visit0,ra,dec,pa,designName keyword. This will give Gen2 enough information to start a SETUPFIELD command. And that will call PFS with fps moveToPfsDesign and the associated agc commands.

The iic declare command will likely also call an ETS finalization routine, but that is to be added later. Since the finalize step is secondary, I propose that we call this IIC command by the more general declareCurrentPfsDesign id=N.

ICC does not care where this is called from. I personally imagine some PFS tool doing so.

When some as-yet-undefined iic finishField command comes in, the iic.pfsDesign keyword should be generated with none/null/nan fields.