Deprecate #register*Callback: methods

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Currently there about about 10 #renderSomethingCallback: methods on
WACallbackRegistry, each of which simply calls "self storeCallback:" with
an instance of the appropriate class.

Excluding tests of WACallbackRegistry itself, *every* sender of these
methods is of the form "aCanvas callbacks registerSomethingCallback".

Additionally, almost every sender of #callbacks is of the form "aCanvas
callbacks registerSomethingCallback".

Since all Renderers have a RenderContext and all RenderContexts have a
CallbackRegistry, I suggest we move these methods onto WARenderer. This
will eliminate having to send #callbacks everywhere and mean that Renderers
have the opportunity to override the type of callback that is registered
(there is currently no easy way to specify that a subclass of
WACallbackRegistry be used).

Existing implementations could possibly be left as "deprecated" if desired,
though they would have to duplicate the implementation.

Original issue reported on code.google.com by jfitz...@gmail.com on 6 Feb 2009 at 2:17