Make the event types more robust

[L-Henke]

I think that the event type should be an Integer and not a string, because it is probably faster to switch on an integer than on a string. This is widely used in other event systems (e.g. Android request codes in startActivityForResult)

[thechauffeur]

Maybe we should leave this for now. We need a process to register event types (e.g. for modules) anyway and could then improve the way this works.

[thechauffeur]

We think about using objects for this. More thoughts are required about how to access an event type etc.

HOW TO:

• differentiate event types
• register event types

[thechauffeur]

@schulze and @L-Henke want to discuss this.