[add|remove]Listener are superseded by connect/disconnect and should be removed

[sjmiles]

Before pure dojo.connect/disconnect were merged with the DOM-aware listener logic, dojo.[add|remove]Listener were public functions.

Now, connect/disconnect are preferred and have a cleaner API (disconnect only takes one argument).

I plan to remove [add|remove]Listener from the public API because I believe they only add confusion at this point.

[bill]

(In [8482]) Change addListener() calls to connect(). Refs #2934. Still need code to collect all things that need to be disconnected on widget destroy.

[sjmiles]

(In [8918]) Privatize add/removeListener, client code should just use connect/disconnect. Refs #2934.