Similar to the ably-java implementation of the same class, checks the message
extras and a few other fields on the message to check that they match the user-provided
filter.

This class will be used as part of a message filterer to implement filtered message
interactions.

Rather than manage filtered listeners directly in the channel class, which makes it awkward to test
in isolation, the ARTFilteredListeners class separates out this behaviour.

Also adds a filtered listener class that applies the filter before calling the
listener.

This change implements the message interactions specification RTL22 for the ARTRealtimeChannel class.

Includes a method to subscribe a listener with a filter as well as one to remove listeners based on the
filter they have associated with them (if at all).