Allow for callbacks pre and post from web service calls

[sfloess]

Simply allowing for trapping exceptions on SOAP faults is insufficient.

We should also allow for both pre-call and post call processing:

• it may be nice to externalize the return values by external implementations. If there are special return values from web service calls that require failure this will allow that processing externally from Keraiai.
• allows externalization of both "the act of calling" as well as "the act of returning"

We probably want to allow for both a static as well as per instance callbacks.