BotkitConversation ignores {type: typing} messages

[benbrown]

The BotkitConversation class has a few issues that prevent non-message type events from passing through.

First of all, messages without text or attachments are ignored. Need to fix this, at least, to also allow messages with a type set:
https://github.com/howdyai/botkit/blob/master/packages/botkit/src/conversation.ts#L657

Second, the makeOutgoing method does not currently copy forward the type field.
https://github.com/howdyai/botkit/blob/master/packages/botkit/src/conversation.ts#L787

[benbrown]

Once resolved, the WebAdapter typing feature can be used in a BotkitConversation like this:

    let typing = new BotkitConversation('typing', controller);

    typing.say('I am going to type for a while now...');
    typing.addAction('typing');

    // start the typing indicator
    typing.addMessage({type: 'typing'}, 'typing');
    // trigger a gotoThread, which gives us an opportunity to delay the next message
    typing.addAction('next_thread','typing');

    typing.addMessage('typed!','next_thread');

   // use the before handler to delay the next message 
    typing.before('next_thread',  async() => {
        return new Promise((resolve, reject) => {
            // simulate some long running process
            setTimeout(resolve, 3000);
        });
    });

    controller.addDialog(typing);

    controller.hears('typing dialog', 'message', async(bot, message) => {
        await bot.beginDialog('typing');
    });