Rm lang key "caching_dir_public"

check for php 7.3

This key isn't used since f394a34c . Removing
it ensures translators don't bother translating it for nothing

php 7.3.0 is released on dec-06-18.
http://php.net/ChangeLog-7.php#7.3.0

added badges for number of issue, release and license. It will give quick info to users about q2a project.

Fixes glitches/ugliness on Windows

Corrects 1.8.0-beta and 1.8.0 being treated as the same version.

Add localization to plugins under qa-plugin

Fix #709

Added checkmark to admin labels

 Extract closed question check into own function

Add ^site_url as a fixed substitution placeholder when sending email notifications

Remove some unnecessary SQL queries

Turn all remaining AJAX calls in admin into JSON

Use JSON in admin_click AJAX calls