Add shutter line to OO version

[raacampbell]

Add a digital output line that turns high or low at the onset of scanning to open or close a shutter. The additions should be implemented as follows:

• [x] Add a property called shutterLine that, if present, will use this particular DIO line control the shutter.
• [x] Add a property called shutterOpenTTLState that determines if the TTL line going to the shutter should be high or low when the shutter is open.

[raacampbell]

This will need to be a separate session. Adding to same session will not work across boards. e.g. the PCI-6110 has no hardware clock on the digital lines so adding digital lines to the same session will reduce the clock rate to the speed of the lowest clock (which is zero because there's no clock on the digital lines).

[raacampbell]

This is implemented on the acquisition PC.

[raacampbell]

Yep, this works.