#207 adder method for collections on target

For review, it is not yet completely finished. It contains TODO's in the `MapperCreationProcessor.java` and `Type.java`. It also lacks more unit test (placeholders are in place).
> I'm still not clear when Dali is doing this deduction. In which situation does this happen?

Dali generates code. It uses Column names to generate getters / setters. I'm not an expert here, but I think it pluralizes the column names.  So we need to do the reverse to find a match in case of ambiguity.


> Shoudn't we try to apply the correct form first? I don't think we really should assume the usage of any specific tool such as Dali, but I guess it doesn't do harm to do it as some kind of fallback.

Done as proposed.