WIP Refactoring of exceptions:

1) All slicer's exceptions are now derived from Slic3r::Exception.
2) New exceptions are defined for slicing errors.
3) Exceptions are propagated to the Plater to show.
It remains to modify the slicing back-end to throw the new SlicingError
exceptions instead of std::runtime_error and to show the other exceptions
by a message dialog instead of a notification.

src/slic3r/GUI/ConfigExceptions.hpp

@@ -1,15 +1,15 @@
 #include <exception> 
 namespace Slic3r {
 
-class ConfigError : public std::runtime_error { 
-using std::runtime_error::runtime_error;
+class ConfigError : public Slic3r::RuntimeError { 
+	using Slic3r::RuntimeError::RuntimeError;
 };
 
 namespace GUI {
 
 class ConfigGUITypeError : public ConfigError { 
-using ConfigError::ConfigError;
+	using ConfigError::ConfigError;
 };
-}
 
-}
+} // namespace GUI
+} // namespace Slic3r