Add option to disable default startup message

[JoshuaKlassen]

This PR is to add the option to disable the Initializing Botkit vXXX message as per #687

To achieve this, CoreBot.js was modified to check for disable_startup_message on the configuration object.
If disable_startup_message=true, the startup message will not be shown.

Example:

var controller = Botkit.slackbot({
    debug: true,
    disable_startup_message: true
});

Upon getting started, I noticed that .vscode files are not in the .gitignore (I am using VSCode)
If this is intentional let me know and I can undo the change.
My VSCode editor generated a settings.json file, I have added that to the .gitignore incase this is something that should be ignored - if not it can be removed.

[jonchurch]

I'd suggest changing it from a console.log to a botkit.debug instead of adding a new config option to the growing list.

But having a startup message somewhere is a good idea, with maybe botkit' starter kits starting off in debug mode so you at least see the message on your first run.

[JoshuaKlassen]

Sounds good, I'll make the change to a botkit.debug

As for the starter kits, would that be acceptable to make debug enabled by default?

[peterswimm]

Could you explain why setting debug to being on default is preferred behaviour? My gut is that it would be an annoyance for most first time users, and is only really useful for people diagnosing unusual problems.

The initializing message is useful for us, particularly with regards to roadmap plans and supporting problems, and will eventually contain other useful information for developers. but being able to opt-out of receiving them is probably a reasonable request.

[JoshuaKlassen]

I just did what @jonchurch suggested
I can switch it back to a config option if that seems most appropriate

[benbrown]

I like @JoshuaKlassen's original idea - allow the message to be disabled independently of debugging. I believe this IS important to be on by default.

[JoshuaKlassen]

I reverted back to original idea. I also felt it would be appropriate to make the config option plural, seeing as how we could add more startup messages in the future

[jonchurch]

👍 Sounds good to me.

@peterswimm I agree, that would likely annoy developers. I was suggesting a scenario where the startup is on by default, but dependent on debug mode.

Y'alls solution is cleaner and more predictable though.

[JoshuaKlassen]

@peterswimm, @jonchurch, @benbrown: is there anything I am missing, or is this good to go?