Update ContentNodeBinder interface to make it more clear

The bind method of the ContentNodeBinder interface accepts the content to bind as an Object. When I asked why, Woonsan replied:

"Actually WorkflowPersistenceManagerImpl#update() would
throws an exception like the following if it is not a HippoBean:

} else

{ throw new ObjectBeanPersistenceException("The content object parameter should be an instance of HippoBean."); }

Anyway, probably that type was defined by me originally. I thought we
were going to support real POJOs. e.g, instead of extending
HippoItem/HippoDocument/..., defining pure POJO interfaces or classes
with annotations.

Anyway, that API doesn't seem to have been touched ever from the initial
design."

The improvement would be to add a new method like this:

boolean bind(HippoBean content, Node node) throws ContentNodeBindingException;

And deprecate the exisiting one. Makes what you need to do more clear, and anything else then a HippoBean won't work anyway.