Take care of negative rotation values
driver: change C unit to °C

Now that all the clients support unicode, we can write °C correctly.
Fail if more than one spots are detected
gui canvas: don't fail if no image available and trying to find out the FoV
gui settings: don't show e-beam magnification if horizontalFoV available

make control_type support to be callable, like choices

Use this to determine whether magnification is useful for the user.

also some small cleanups
Merge branch 'kimon-MiniCalibration' of vpn.delmic.com:odemis into kimon-MiniCalibration
Merge branch 'master' into kimon-MiniCalibration