Redisbridge

* Change behavior of `RedisBridge.init()` to spin up local Redis server only if the specified host was localhost
* Minor updates to `RedisBridge` class, including the option to manually connect to Redis server after bridge creation
* Fix bug with blocking requests on unsubscribed channel

* Add `register_callback()` and `deregister_callback()` methods to `RedisBridge`
* Deprecate `CallbackDecorator` alias
* Bug fixes

* `RedisBridge` replaces the `dummy_redis_server` keyword argument with `use_mock_redis_server`
* Better error handling when connecting to Redis server, with fallbacks in the following order:
1. Try to connect to specified host
2. Automatically spin up local Redis server (if needed) and try to connect to localhost
3. Connect to a mock Redis server

* Switch message encoding to JSON to support cross-language serialization
* Deprecate `callback_decorator()` method from `RedisBridge`
* Other minor tweaks & bug fixes