AccessoryViewRevealer should allow for right AND left pan/reveal

The `AccessoryViewRevealer` provides the functionality to expose the time of message (based on it's default implementation).

It should provide functionality to instruct a delegate that a pan has been made in a desired direction (left or right), the delegate would then decide what action should be taken based on the current state.

The `AccessoryViewRevealer` should then be able to manage the "exposed left/right" state and return it to a "normal" state when "panned" in the opposite direction, if the delegate doesn't reset the state to "normal" automatically

I'm happy for the `AccessoryViewRevealer` to continue to calculate when a reveal should take place, but this functionality could also be provided by a delegate for easier extendablility

Start by locating AccessoryViewRevealer and read how it currently detects and exposes a pan. Trace its delegate interactions and state handling. Done means delegates can be informed of left and right pans, the revealer tracks either exposed side, and an opposite pan can return it to normal when needed.

Written by the indexing model from the issue text.