Notify the main bot code if we didn't find a matching item

[jcocchi]

If we collected values for all parameters and the user still didn't find an item they want, we currently send a "no items found" message to the user and return control back to the bot. Most likely, bots using this library will need to know if the user found a gift or not.

Figure out the best way to communicate this- maybe send back an error message.

[jcocchi]

Send a noItemsFound action back to the bot and write documentation to tell users how to handle this case. Most likely a noItemsFound dialog with a trigger action listening for this notification from the library