Updates to the WhyLabsCallbackHandler and example notebook
- Update dependency to langkit 0.0.6 which defines new helper methods
for callback integrations
- Update WhyLabsCallbackHandler to use the new `get_callback_instance`
so that the callback is mostly defined in langkit
- Remove much of the implementation of the WhyLabsCallbackHandler here
in favor of the callback instance
This does not change the behavior of the whylabs callback handler
implementation but is a reorganization that moves some of the
implementation externally to our optional dependency package, and should
make future updates easier.
@agola11
