Add a linter rule to detect static method calls which should reference the parent class instead of a hardcoded class reference. For example, consider the following:

class SomeClass extends AnotherClass {
  public function someMethod() {
    AnotherClass::someOtherMethod();
  }
}

This should instead be written as:

class SomeClass extends AnotherClass {
  public function someMethod() {
    parent::someOtherMethod();
  }
}

Added unit tests.