Abandon Task Feature

* Added abandon task stage option to options page
* Added abandon task button in task encounter stage (uses dynamic naming option above)
* Added the `go_task_abandon()` function to go_pnc.php
 * 5 parameters: `($user_id, $post_id, $e_points, $e_currency, $e_bonus_currency)` to be used elsewhere.  The abandon task button uses AJAX to call the `go_task_abandon()`
* Removed `go_award_badge` shortcode from the shortcode list in the task edit page