Bonsai-python

Added
- Add code coverage configuration.
- Add a `selection` field to the `SimulationSourceData` protobuf message for
internal Bonsai platform use.

Removed
- Remove the `MessageBuilder` class, but keep its reconstitute methods as
normal functions.
- Remove parsing of the `--headless` argument. This argument is now parsed
by the functionality in the bonsai-gym-common class.

Added
- Add an error if API access key is missing.
- Add support for specifying required arguments via environment variables.

Added
- Add support for specifying an access key using the `--access-key` command
line argument.

Added
- Add support for internal Bonsai platform integration testing.

Fixed
- Fix a bug which would cause KeyErrors raised when simulators return
incorrect state dictionaries to be incorrectly caught.

Fixed
- Fix a bug which would cause certain KeyErrors to be incorrectly caught
as unexpected message errors.
- Fix some pylint errors.

Added
- Add support for creating `Luminance` objects from additional data types.
- Add ability to support batches of predictions and states when
communicating with the Bonsai server.

Changed
- Large refactor to better support internal Bonsai platform system testing.
This refactor adds asyncio support when using python 3.5.

Fixed
- Fix a bug which could cause a simulator to hang when it should exit.