make methods of local distributed eventbus virtual

[tntwist]

Description

I need to override several methods of the local distributed eventbus.
So i just made all methods virtual to allow overriding necessary methods.

Checklist

• [ x] I fully tested it as developer / designer and created unit / integration tests
• [x ] I documented it (or no need to document or I will create a separate documentation issue)

How to test it?

There should be no testing needed, since it does not change anything in the framework. It just gives possibilities for customizing some logics.

[nebula2]

finally!