Async output: stop being so dramatic

Yes, ClosedByInterruptException isn't really something we want to see.
Print a warning, though, not a stack trace, 'kay?

Signed-off-by: Luke Stuyvenberg <stuyvenberg@wisc.edu>
Added experimental Picard metastage device

Essentially, this implements the idea I had in my comment on issue 120 on
the bugtracker. The new 'device' creates two CSIABStage instances and
bundles them as an X/Y stage.

I'd like to stress that this is experimental, and shouldn't be relied upon
for anything yet. In fact, prior to any uploads of the PicardStage DAL, it
may be wise to comment out the 'AddAvailableDevice' call so it doesn't
show up.

Signed-off-by: Luke Stuyvenberg <stuyvenberg@wisc.edu>
Caught twister/stage null pointer issue

Under some weird circumstances, starting the hardware config wizard could
cause crashes. It turns out that things like GetPosition were still being
called after ShutDown, which freed the twister/stage handles. I've added
checks, though this should probably be investigated further.

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