Update extension policy

WEBSITE-1078
Add requirement for extension module auth to policy
Merge pull request #55 from VSEphpbb/task/31x-extensions

Update extension policy
Change Core Events to PHP Events

WEBSITE-1078
Merge pull request #56 from VSEphpbb/task/31x-extensions

Change Core Events to PHP Events
Remove 3.1 launch block in the header

WEBSITE-1188
Merge pull request #40 from PayBas/task/remove-header-release-block

Remove 3.1 launch block in the header
Update merge script
Update scripts
Changes to merge.sh documentation
Fix Twig docs typo for style creation page

WEBSITE-1146
Retry if composer/security check fails (github & security checker)
Merge pull request #41 from michaelcullum/master

Retry if composer/security check fails (github & security checker)