Issues Addressed:
Created cron task that will check if there is a newer version of e107 available. If so, email site admin, create log entry and trigger message for site admin

Files altered:
e107_admin\cron.php
e107_handlers\cron_class.php
e107_languages\English\admin\lan_cron.php

Related to:
https://github.com/e107inc/e107/commit/20cb65f53936155210ab75475ff1f5f59d1f71b1
Merge pull request #281 from jburns131/checkCoreUpdates

Check core updates
Closes #283 whitelist <script> attributes and noscript tag (when script posting is enabled)
Issue #283 target attribute is valid in html5
Display upgrade alert on main admin page only.
Improved logging of the upgrade process.
Code cleanup on usertheme_menu. Very outdated.
Some userclass fields didn't support class ID>255, visibility needs to support 'not member of...'. Possible tenuous link to Issue #266
Issue #268 - graceful retreat if CURL not installed on getRemoteFile()
Fixes Issue #266 item 4