OOTB: Provide an option to globally disable the personal contact forms, and make it the default for new installations

This feature request is a follow-up to this bug report: #6064

@klonos

...I think that there should be a "Disable all personal contact forms" setting.

@jenlampton

I have always wanted this for contact module. And it should be disabled by default!

@kiamlaluno

I guess it would make sense in the case a site plans to use the Contact module just for the site contact form.

@olafgrabienski

Let's try to avoid "Disable to enable" situations. If it turns out that we need the setting, it should be "Enable personal contact forms".