Make CachingComponentAdapter more reusable

Hi, i copied the ObjectReference interface from the pico integration kit to the pico project and made CachingComponentAdapter use it internally or if requested otherwise the one supplied in the constructor.

Sample:

new CachingComponentAdapter(new ConstructorComponentAdapter(stuff));

will cache the instance in a serializable class just like it used to.

new CachingComponentAdapter(delegate, new AppScopeObjectReference("key"));

will cache the object in an ServletContext attribute referenced by "key". [see picoextras-servlet].

I believe that storing the reference inside the componentAdapter isnt always the best choice and by applying this it will just let you choose to do it or not.

All tests passed too.