Merge branch 'master' into major

Conflicts:
	CHANGES.md
	dev/builder/build.sh
Widgets without buttons won't be added to ACF.
Changelog entry.
Merge branch 't/11567b' into major
Don't try to select non-editable elements on mousedown.
Changelog entry.
Merge branch 't/11727' into major
Introduced filter#disallow.
Got rid of filter function's caching wrapper which was unncessary.
Refactorised the form of processing function to open it for new options.
Extracted code doing actual filtering to a separate function.
Extracted code applying transformations to a separate function.
Updated functions order (asc name).
Added entire elements disallowing.
Removed old leftover - element name validator for a generic rule is not supported.
Minor simplification.
Filter out properties which are disallowed by ACF.
Cleaned up a leftovers - none of validator functions check values.
Introduced config.disallowedContent.
Filter#addFeature checks the feature if any disallowed content rules are defined.