This also resulted in a refactoring of the Providers and parsing
Exceptions. NumberFormatException and ParseException can now be thrown
directly, the wrapping in a SmackParsingException is down at a higher
layer, i.e. in AbstractProvider.
This also moves the logic to send error IQ replies from "when there is
no IQ provider registerd" to "when there is no IQ request handler
registered". Which has for example the advantage that IQ parsing no
longer asks for a connection instance.