Add Opcache status monitor

[freephile]

Added opcache.php (and data-sample.php) from https://github.com/rlerdorf/opcache-status.git into the ServerPerformance files. (htdocs role)

However, I changed the opcache.php script to use our already-in-use jquery and d3 in the ServerPerformance directory. Rasmus' version pulls files from cloudflare which is not ideal. In a quick test of functionality, it seems to be happy with js library versions.

<script src="//cdnjs.cloudflare.com/ajax/libs/d3/3.0.1/d3.v3.min.js"></script>
<script src="//cdnjs.cloudflare.com/ajax/libs/jquery/1.11.0/jquery.min.js"></script>

changed to
./js/d3.js (v 3.5.14)
./js/jquery-3.1.0.min.js

data-sample.php just provides a mock implementation of the opcache functions in case opcache is disabled - so you get a chart instead of an error. There are no external resources.

##Testing
See https://demo.qualitybox.us/ServerPerformance/opcache.php for an example.

##ToDo
add some sort of restriction on who can access /ServerPerformance

[jamesmontalvo3]

@freephile merging this into the opcache branch I merged #943 into.