ESSENTIALS-398: preps.
ESSENTIALS-398: new UI + backend for content blocks.
ESSENTIALS-398: adjust content blocks UI.
ESSENTIALS-398: more content blocks improvements.
ESSENTIALS-398: Layout improvements.
ESSENTIALS-398: Extra pointer to documentation.
ESSENTIALS-398: move existing fields check to correct location.
ESSENTIALS-398: move existing fields check to correct location.
ESSENTIALS-398: Improved filtering for document (and compound) types.
Merge branch 'master' into ESSENTIALS-398