Support "online" and "offline" OCSes.

PFS will want to be able to run (take exposures) anytime, whether allocated or not, whether on the telescope or not.

Discussions yielded:

• PFS will have an "online" and an "offline" OCS. The online one is the real operational Subaru copy, the offline one is something which PFS will run, can connect to, and will let us never worry about interfering with observations by other instruments.
• Subaru will come up with a single frame counter accessible to both.
• PFS will come up with a way to seamlessly and quickly switch between the two. "gen2 online"/"gen2 offline" is the way I think of it.
• The offline OCS should be clever about headers: what to provide, what to declare, what to lie about.

This ticket should simply defer to at least two others: for the Subaru OCS work and for the PFS ics_gen2Actor work.