Add concept of system information page

Add information about current software versions, server software, php
extensions loaded, and database space usage.

In the future, this will offer a nice place to add an import/export button
for data backup and restore, announcements, and more
Merge pull request #98 from greezybacon/feature/system-info

Add concept of system information page

Reviewed-By: Peter Rotich <peter@osticket.com>