Make it easier to enter a URL during `ghost config`

[ErisDS]

At present we expect a fully formatted URL to be entered during ghost config including the protocol. However, we don't really make that clear in all cases and it's not really required. It's perfectly reasonable for me to enter mysite.com and expect that the CLI would add the https part for me along with setting up SSL.

Instead, what happens currently is the CLI complains the URL isn't valid 😞

I think we should add protocols to the URL according to the following rules:

• if the url entered is localhost, or an ip, add http
• if the url entered is a domain, add https

Note: we are moving as fast as we can towards only supporting http for development - all Ghost blogs should be run fully HTTPS in production.

[acburdine]

As a side note this actually might allow us to upgrade our version of validatorjs, which is currently pinned a few major versions behind due to them changing the url validation.

Not that we have to update it, but if this change allows us to we might as well.