prereq and dependency checks on post trash

[thomasplevy]

use action wp_trash_post (https://core.trac.wordpress.org/browser/tags/4.5.3/src/wp-includes/post.php#L2656) to perform lookups before trashing

Also check into untrash actions

course

• [ ] remove prerequisites from any other courses
• [ ] remove from membership auto-enrollment
• [ ] cancel enrollments?
• [ ] delete child sections
• [x] remove access plans (on deletion) (via #1518, #1522)

sections

• [ ] unset lesson parent meta data

lesson

• [x] remove prerequisites from any other lessons
• [ ] warnings on builder when lessons deleted (empty node on syllabus)

quiz

• [x] remove from any lessons
• [x] remove quiz attempts

questions

• [x] remove from any quizzes

track

• [ ] remove prerequisite from any courses

membership

• [ ] remove restriction settings from any post which supports membership restrictions
• [ ] remove from members-only access plans
• [ ] check and remove from site wide restriction setting
• [ ] cancel enrollments?
• [x] remove access plans (on deletion) (via #1518, #1522)

~user~

• ~postmeta cleanup~
• ~order anonymization~
• ~cancel recurring orders~

User cleanup moved to #940

orders

• [x] related transactions

WIP: https://github.com/gocodebox/lifterlms/blob/master/includes/class.llms.post.relationships.php

[thomasplevy]

Transactions should be deleted when an order is deleted

[eri-trabiccolo]

@thomasplevy we should remove access plans when "parent" course/membership is permanently deleted, as we don't have the concept of an "orphan" access plan. Should we add this to the list above or should we open a new issue?

[thomasplevy]

@eri-trabiccolo added above