Add interface for logging

There is currently no mechanism for logging of error, warning and info messages in MantleAPI. Therefore the OpenScenarioEngine logs all messages to the console using std::cout, which is not convenient for the user. I would like to introduce a new Interface in MantleAPI with the following use case:

The simulator should be able to display logging messages of the scenario engine in its user interface or write them into a file.

The interface should be able to distinguish different kinds/levels of logging messages, e.g. error, warning, info.