fix(pageowner): allow unsetting of page owner guid

fixes #7278
Merge pull request #7345 from jdalsem/unset-page-owner-guid

fix(pageowner): allow unsetting of page owner guid
docs(design): added the data model image from docs

ref: #7552
docs(general): moved pronuncation file from docs

ref: #7552
chore(docs): replace hardcoded link to learn.elgg.org with internal
reference

ref: #7552
Merge pull request #7593 from jeabakker/leftover-docs-issue

Leftover docs issue
chore(uservalidationbyemail): change ['login:after', 'user'] to ['login:before', 'user'] event
Merge pull request #7602 from iionly/issue-6493-3

chore(uservalidationbyemail): change ['login:after', 'user'] to ['login:...