[Form] [Util] [PropertyPath] Added __call method to property path

Bug fix: no
Feature addition: yes
Backwards compatibility break: yes (it might be a problem when class has __call and __get and __set method)
Symfony2 tests pass: yes
Fixes the following tickets: no ticket
Todo: no todos
License of the code: MIT
Documentation PR: The situation with magical method is not probably described in documentation.