Error raised while loading scripts
When a script is loaded, errors may appear. For instance, ImportError
if the script is using a non-installed script.
While these scripts shouldn't be added to the GUI, user should be able to know which scripts are unavailable, and why.
Currently, biseau package does not provide any way to get an InvalidScript object, but it will be done soon. The GUI should show them, or at least the errors raised by biseau.