Test new validation logic

thumbnailDirectory -> thumbFolder

Partials, pages and content now support drag'n'drop

Strip indexes from repeater data sets

Allow external group field definition - Refs octobercms#2772

Add mergeConfig helper, useful for extension

Refs octobercms/docs@8575ece

Move extension validation to files only

Block media manager entirely if user lacks access

Fixes recordfinder (again)

Lots of complicated stuff going on here, all elements are getting wiped out when a record is updated and the control is getting disposed at the same time. We've created a dedicated variable to store the datalocker name as a string, this represents a small memory leak but a necessary one it seems.
Fixes octobercms#2798

Move the change event to the input element

This should bubble to the parent control element and persist any logic that depends on the old event
Fixes octobercms#2684