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/FirmwareDialog.cpp

@@ -766,7 +766,7 @@ const char* FirmwareDialog::priv::avr109_dev_name(Avr109Pid usb_pid) {
 			return "Original Prusa CW1";
 		break;
 
-		default: throw std::runtime_error((boost::format("Invalid avr109 device USB PID: %1%") % usb_pid.boot).str());
+		default: throw Slic3r::RuntimeError((boost::format("Invalid avr109 device USB PID: %1%") % usb_pid.boot).str());
 	}
 }