Add per-lamp time cards for DCB

Add per-lamp time cards for the DCB lamps, modeled on the pfiLamps design. Do not add the measured flux cards (yet). In other words, for the following, we just want W_DCNET, etc.

So the DCB could generate keys like, say, neonLamp=time,flux, and probably some attenuator cards or fields when that system is understood.

Note that for the purposes of lamp-controlled FITS header cards, the keyword should be correct either at the start of integration or at the start of readout. Currently the cards are grabbed at the start of integration, so if we keep to generating the "on" keywords at the dcb prepare stage and "off" ones at the end of the dcb go stage we will be OK.

I don't see us putting in the engineering time to measure the actual exposure times for this PDU, so I propose just reporting the requested time. For the pfiLamps controller that will be exact.

== From pflampsActor design doc:

For a given lamp (neon, say):

• W_CLNET, a float, states the requested lamp on time. 0 means off.
• W_CLNEV, a float, shows the lamp's component of the measured photodiode voltage.

The HgCd lamp is slightly different. We control a single HgCd lamp, but measure a mercury line and a cadmium line independently. So for that lamp, there will be:

• W_CLHGCC, the float for the commanded HgCd lamp state.
• W_CLHGV, the measured Hg photodiode voltage
• W_CLCDV, the measured Cd photodiode voltage