[4.0] Bump to PHP 7 minimum

[mbabker]

Summary of Changes

Bump 4.0 to PHP 7 per yesterday's announcement

Documentation Changes Required

Add the new minimum to the B/C page

[zero-24]

Here is the article: https://developer.joomla.org/news/704-looking-forward-with-joomla-4.html

[mbabker]

FWIW the Travis failure exists in the base branch too. So the only thing that should be stopping this for the moment is making sure I didn't completely destroy the AppVeyor config.

[wilsonge]

Holding off on merging this just now until I've finished my round of conflicts i'm about 2/3 of the way through

[zero-24]

FWIW the Travis failure exists in the base branch too. So the only thing that should be stopping this for the moment is making sure I didn't completely destroy the AppVeyor config.

see here for the travis issue: #17550

[zero-24]

Given that the travis error is a different on #17550 I'm not sure what did happen to appveyor here. Do you have a way to restart the build?