add a simulation mode based on the fixture pool

it's very tricky to actively test the UI because you can't just inject
arbitrary SMART data blobs.

this refactor seeks to remedy that by abstracting away the device
notification from solid and based on that implement a complete
simulation mode where both the device notifier (the bit enumerating
solid) and the ctl (the bit doing kauth + smartctl) are replaced by
mocking instances at runtime. these instances then use the data in the
fixture pool instead of actually looking at the active hardware on the
system. this effectively allows us to check how all the various fixtures
are actually handled by the actual production code.

for convenience more than anything this is on by default when building
in debug mode. also for convenience the fixtures are rcc'd into the
binary instead of looked up from disk (also relocatability is of course
always a concern)

(this actually reveals a problem with the notification tech: it doesn't
notify on devices that are failing right out the gate since a fix that
changed how devices are added to the monitor :()