If running on host, and no iio devices, check before you use things, so
it doesn't emit warnings.

signed-off by: Robin Getz <robin.getz@analog.com
Don't always require the builder to be sent down, this way we can do
things a little easier in some of the plugins.

Signed-off-by: Robin Getz <robin.getz@analog.com>
Add a threading model, so plugins can access data
Still needs a little TLC.

Signed-off-by: Robin Getz <robin.getz@analog.com>
Add a dialog for calibration, which uses the threading model, to get and
examine data. Still needs a little work.

Signed-off-by: Robin Getz <robin.getz@analog.com>