Issue 43: add exception catching code only for non-debug builds

The intent for the code added for issue #43 (closed) was, that if an error while running BornAgain occured, to make it more apparent to the user. As it turned out, this resulted in a drawback for the developers: if BornAgain is run in a debugger and an exception is thrown and subsequently displayed in the message box, the program stops at piece of code, where the whole information, where the exception was thrown (call stack) is not there anymore.

To improve the situation, this MR contains code which only adds the exception catching code for non-debug builds. I.e. in release builds, if an exception is thrown, a message box will be presented to the user (as before) and in debug builds, the exception will not be caught and can be analysed in the debugger just like before the implementation of issue 43.