Dave watchdog timer

[HazenBabcock]

Add a timer to Dave which will go off if HAL does not respond to a message in the expected time. This would be a warning? Error? At least an e-mail to the user to let them know that their run may have frozen.

[seichhorn]

@HazenBabcock I believe I'm encountering an issue related to this. My stage is running slowly, and on relatively long moves, the watchdog timer was triggered and I'd see "> stage move request timed out" in the Hal command prompt. From the comments in the handleWatchdogTimer I thought this should just continue on, but it seemed like it messed up some aspect of confirming focus, and after this event the focus lock stopped reporting values/updating itself.

Extending the duration of the watchdog timer seemed to resolve the issue for me, but thought you'd want to know about this as this seems like unexpected/undesirable behavior.

[seichhorn]

I actually think this wasn't my issue, it just happened to coincide with when the focus scan event occurred #97