Rethink and unify error handling

[manuel-mauky]

At the moment the error handling isn't optimal. In some cases we simple log an error message and return null in error cases.

For example, when you have a NullPointerException in one of your initialize methods you only get notified when you have logging configured. The reason is that such exception is encapsulated into an IOException by the FXMLLoader's load method and we are catching IOExceptions in our ViewLoader.

This is only an example. In general we should think about rules on when to (re)throw exceptions and when to just log them.

[manuel-mauky]

In some of the last issues (f.e. #97, #84, #83) we have already changed the exception handling in many cases.
As far as I can tell the last place where no exception is thrown and only a message is logged is when an Exception is thrown in an implicit initialize method for JavaViews. At the moment this exception will be catched and only logged.

I will change this behaviour now.