Make ERROR_404_HELP = False by default

[wswld]

I encountered an issue with ERROR_404_HELP occassionally and found it to be extremely counterintuitive (that one code behaved completely differently than the others) and underdocumented. My suggestion is to make it:

help_on_404 = current_app.config.get("ERROR_404_HELP", False)

I can provide a pull request if required.

[mrkmcknz]

I second this.

[joshfriend]

I always turn this off too as I don't find it helpful. I'd rather remove it completely TBH.

[wswld]

Provided a pull-request. Please check it out.