Automatic opening of fast shutter

[canismarko]

Beam damage may be a big problem for operando experiments. One easy solution is a fast shutter that stays closed and only open briefly when actually triggering a detector. Bluesky makes this easy, since we can intercept and inspect messages as they go by. For example, this plan produces the following messages:

bp.count([ic], num=2) (assuming ic is a device)

'stage',
 'open_run',
 'checkpoint',
 'checkpoint',
 'trigger',
 'wait',
 'create',
 'read',
 'save',
 'checkpoint',
 'checkpoint',
 'trigger',
 'wait',
 'create',
 'read',
 'save',
 'close_run',
 'unstage'

The strategy can be:

1. Watch for "trigger"
2. Yield Msg("read", shutter)
3. check the return value to see if the shutter is closed
4. If it was yield Msg("set", shutter, 0)
5. Yield the original trigger
6. Watch for the subsequent wait message
7. Afterwards, yield Msg("set, shutter, 1) if the shutter was originally closed

One tricky bit, not all plans and not all devices need this behavior. We can make it a plan decorator, but then we need to know which devices have this requirement.

[canismarko]

Added this support in #338