#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).
```java
   /**
     * Tries to find an addMethod in this type for given collection property in this type.
     *
     * Matching occurs on:
     * <ul>
     * <li>1. The generic type parameter type of the collection should match the adder method argument</li>
     * <li>2. When there are more candidates, property name is made singular (as good as is possible). This routine
     * looks for a matching add method name.</li>
     * <li>3. The singularization rules of Dali are used to make a property name singular. This routine
     * looks for a matching add method name.</li>
     * </ul>
     *
     * @param collectionProperty property type (assumed collection) to find  the adder method for
     * @param pluralPropertyName the property name (assumed plural)
     *
     * @return corresponding adder method for getter when present
     */
````