Added an inteface HasAttribute which can be used for any class to serial...

In EasyWsdl.com we've implemented Array type for RPC encoded web services (more info here http://publib.boulder.ibm.com/infocenter/wmbhelp/v7r0m0/index.jsp?topic=%2Fcom.ibm.etools.mft.doc%2Fbc19050_.htm).
For this we must write some attributes to soap message but we can't inherits from AttributeContainer class (because we already inherits from Vector). With this refactor we can now implement HasAttribute interface and write any attributes we want (AttributeContainer class also implements it).

This refactor is safe and shouldn't break compatibility with any existing code