Upgrade to PHP 7.1.0

Summary:
To continue to offer an up to date CLI PHP environment to Docker
containers to run Arcanist, phpunit and other PHP apps, we jump
from PHP 5.6.29 to PHP 7.1.0.

Some features were missing from PHP 7.0 branches, like PCNTL signals,
and some users was so more confortable to wait PHP 7.1. We've tested
CLI applications behavior with this version since December, we're
fairly happy with the results.

Legacy PHP 5.6 apps will be able to use our 5.6.29 tag, and ask us
for migration support to migrate to latest.

Upgrade process is similar than e07d5b80404.

We add APCu too, as this image is used for CI purpose and we take
responsibility to provide a comprehensive PHP environment.

Some unmaintained PECL extensions, newt and ncurses are removed.

Test Plan: Build, rebuild nasqueron/arcanist

Reviewers: Sandlayth

Reviewed By: Sandlayth

Maniphest Tasks: T1072

Differential Revision: https://devcentral.nasqueron.org/D764