#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).
No. Dali has a simple set of rules. It therefor makes the wrong deductions on plural / singular form. MapStruct now first tries to match up to these wrong deductions made by Dali (on the premise that this is the most used framework for entity-jpa code generation). 

If no addMethod is found based on the same set of rules as Dali, Maptruct resorts to a set which is more elaborate (and more Human like) to find a match. This comes into play when the user has corrected the Dali generated singulars or made them himself in the first place.

Note: the matching of the proper add method based on these rules (Dali followed by 'human') is only done in case when ambiguous matches were found based on the method arguments in order to resolve the conflict.