Remember last output directory

A minor convenience feature.

Signed-off-by: Luke Stuyvenberg <stuyvenberg@wisc.edu>
Play nicer with missing stages

When MM first starts, the user won't have a configuration -- if the plugin
autostarts as it now is meant to, it shouldn't expect the stage to exist.

Signed-off-by: Luke Stuyvenberg <stuyvenberg@wisc.edu>
WIP: Restore continuous acquisition

There are significant flaws with it as things stand. Acquisition to disk
doesn't work. Acquiring to memory seems unreasonably slow. I'll be
investigating these things as this commit grows.

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