gui: toolbar in secom + fix zoom to fit with stage

use the new functionality to put a toolbar in the SECOM live view

fix the zoom to fit functionality when recenter is False
gui: add test case for fitViewToContent functionality
semcomedi: improve and fix test cases

test more the config validation (and do it for real)

don't completely fail if the limits are upside down (it's legal!)
semcomedi: fix bug when scanning limits are going down

linspace takes scalars, but if they happen to be an array, the type of the array is used for the step.
If the type is uint, the step can only be positive, and crazyness starts...

Also add a test case to check for regressions.