Add error message middleware

[Stevenic]

This could be done as a sample versus an actual piece of middleware we ship but we need a piece of middleware that you install first in your bot and it listens for an error to be thrown and then simply sends a message to the user telling the something wen't wrong. Other middleware on the stack should have already processed/logged the error so this middleware is just about telling the user something happened.

I think the general strategy we want for all middleware error wise is to handle the error and then re-throw it so someone else can handle it.

In JS I think this middleware looks like:

bot.use({
    contextCreated: (context, next) => {
        return new Promise((resolve, reject) => {
            next().then(
                () => { resolve() },
                (err) => {
                    context.responses.push({ type: 'message', text: `Oops... Something went wrong.`});
                    reject(err);
                }
            );
        });
    }
});

[Stevenic]

Closing this for now as botbuilder-toybox-middleware supports this.