Fix Container property initialization order
Fix Container property initialization order

metadata_encoding needs to be set before the ContainerProxy is
instantiated, because it's read in the proxy's initializer.

Fixes mikeboers/PyAV#265

mikeboers/PyAV,mikeboers/PyAV,pupil-labs/PyAV,pupil-labs/PyAV,pupil-labs/PyAV,PyAV-Org/PyAV,PyAV-Org/PyAV,pupil-labs/PyAV