Improve flexibility of AcqRow

If we wish to have any hope of implementing the IAcquisitionEngine2010
interface, we need to support arbitrary Z slice sets.

Signed-off-by: Luke Stuyvenberg <stuyvenberg@wisc.edu>
fixup! Redundant Asynchronous Output

Signed-off-by: Luke Stuyvenberg <stuyvenberg@wisc.edu>
Continuous mode: Massive framerate increase

Some profiling revealed that the JNI calls to get stage positions for
metadata (which aren't valid in continuous mode anyway) were slowing down
the acquisition by quite a bit.

By moving the continuous acquisition code out of a thread and into the
main acquisition body, and minimizing the potential JNI calls, we can
essentially keep the MM native buffer empty, draining the images straight
to output -- provided the output can accept them fast enough.

Notes:
- The buffer can overflow pretty easily and there is no indication this
  has happened. There is a MM API call that can detect this; a future
  patch will include it.
- Stage position metadata is unavailable/invalid in continuous mode. I
  don't see a good way to obtain it from Java. I will experiment with
  changes in CMMCore to automatically include that information.

Signed-off-by: Luke Stuyvenberg <stuyvenberg@wisc.edu>