Relay error messages to log in GUI

[Jhsmit]

At the moment there is no feedback to users when they, for example, upload a wrongly formatted input data file.

Error messages should be relayed to the logging window via MainController.logger

Also the log viewer could use an upgrade

[Jhsmit]

https://stackoverflow.com/questions/19425736/how-to-redirect-stdout-and-stderr-to-logger-in-python