Support abstract complexTypes - abstract modifier generating

In depend of issue https://github.com/wsdl2phpgenerator/wsdl2phpgenerator/issues/123 I've added a abstract modifier support in this commit, tests included. Hope, you'll agree.
Yes. The reason is to add parameter later than creating an  object. If you look at the creating of PhpClass there are no all parameters from constructor used. I prefer to use a setter than passing null/false/true/empty variables to constructor if my requested parameter is at the end.