Mutation Tokens are not passed to Python Client

It seems that changes in how mutation tokens are handled in SDK3 required the Python SDK to skip propagating the mutation tokens from LCB through the bindings (seems this happened in early release of Python SDK 3.0).

Mutation tokens are available from LCB so the Python SDK bindings needed to be updated.

Notes on Python Bindings (callbacks.c), at the end of the chain is where the handler can be updated w/ mutation token info (after get_common_objects() has been called)

• LCB_CALLBACK_STORE -> durability_chain_common -> dur_chain2
• LCB_CALLBACK_REMOVE -> durability_chain_common -> dur_chain2
• LCB_CALLBACK_SDMUTATE -> subdoc_callback -> dur_chain2
• LCB_CALLBACK_COUNTER -> value_callback (Pending PYCBC-1132)
• LCB_CALLBACK_TOUCH -> keyop_simple_callback