add transitivity check to equals integrity test

[SierraGolf]

background
the transitivity requirement on the equals implementation can only be tested partially when considering one class (the class under test) and is partially covered with symmetry requirement check. in order to allow a transitivity check for multiple related classes there should be an optional test which checks two or more given classes to be transitive to the class under test.

requirements

• the interface should force the user to provide at least 2 classes
• class can but do not have to be related (sharing an interface or being part of the same class hierarchy)

signature
Builder checkTransitivityTo(Class classA, Class classB, Class... otherClasses)