Pass all events to handlers vs noop

[rposborne]

The intent of this pull request is to allow handlers to be able to observe other events such as presence_change. This changes the default behavior of sending unhandled events to a NOOP instead to be a simple passthrough. The entire payload of the event is passed on to the event with no maniuplation.

Possible further steps are to check for standard hash keys and convert them to Lita::User and Lita::Room.

[dmann]

This is great! I'd like to see this expanded to include the 20+ message sub_types that are currently being ignored. Maybe by changing:

        def handle_message
          return unless supported_subtype?

to

        def handle_message
          return handle_unknown unless supported_subtype?

Though, the triggered event would be named :slack_message, so maybe included the sub_type in the event name would be in order. If my suggestions are off topic, I'll gladly submit a separate pull request when this one is accepted and merged in.

[rposborne]

@dmann I think breaking subtypes out might be best as an additional refactor.