FeatureSelection: If the user selects a scale that is too large for the input image, show an error instead of waiting for an error to pop up while the feature is computed.
In conjunction with ilastik/lazyflow@f656d2e5a53b902775dfd7ff3b722e77c5f4a276, this fixes #658.
FeatureSelection: Don't allow the user to select features in the 0.3 scale (except color).
Fixes #610
shell: Better handling of when a project fails to load.
Fixes #739
PixelClassification: Don't allow navigation to other applets while data selection applet is 'busy'