Fixed ListParameter bug when initialized with empty list
Fixes:
  - Camera now reports whether it was able to get precise frame timing in
    a task
  - Scanner uses this flag to determine whether a calibration is valid
  - Scanner calibration 2nd-order fit coefficients are temporarily
    disabled
Fix:  NiDAQ correctly lists devices which can trigger a task
Fixed SutterMP285 limit-setting buttons
Fixed import error in Imager
Disabled closing Manager docks
DataTreeWidget: fixed error caused when dict is updated while being parsed
by the widget (threading issue)