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/libslic3r/GCodeSender.cpp

@@ -153,7 +153,7 @@ GCodeSender::set_baud_rate(unsigned int baud_rate)
 		if (::tcsetattr(handle, TCSAFLUSH, &ios) != 0)
 			printf("Failed to set baud rate: %s\n", strerror(errno));
 #else
-        //throw invalid_argument ("OS does not currently support custom bauds");
+        //throw Slic3r::InvalidArgument("OS does not currently support custom bauds");
 #endif
     }
 }