[ADDE] CSRF validation for Worker Deletion

* [ADDED] CSRF token checks to worker page
* [CHANGED] Check for both _GET and _POST ctokens
* [ADDED] CSRF token to each delete call URL

Fixes #1702 once merged
[IMPROVED] Check if cron is running in PHP scripts

* Ensures we don't spawn more than one PHP process
* Will require admin-intervention to reset the cron_active flag in DB

Shouldn't trigger often but may help people.
Merge pull request #1704 from MPOS/worker-delete-csrf

[ADDE] CSRF validation for Worker Deletion
Merge pull request #1705 from MPOS/cron-check-active

[IMPROVED] Check if cron is running in PHP scripts