[BUGFIX] Add getTransform method to Form Container interface

It appears call of method getTransform in class
Tx_Flux_Service_FluxService can also be made against
a container object. Since the method is not defined in
the PHP interface, a fatal error is raised with message:

    Call to undefined method
    Tx_Flux_Form_Container_Object::getTransform() in
    flux/Classes/Service/FluxService.php on line 478
Merge pull request #331 from fudriot/develop-fix-call-to-gettransform

[BUGFIX] Add getTransform method to Form Container interface