Merge branch 't/9972' into major
Basic sample of data filtering.
Basic dataFilter structure plus configuration loading.
Cachable CKEDITOR.tools.clone and fixed docstr.
Filtering elements - part 1/N.
Validate classes, attrs and styles.
Fixed allowedContent regexp pattern and prevented internal data-cke- attributes removal.
Minor fix.
Minor improvement.
Plugins now add their requirements to allowed content.
Added more features to dataFilter rules to suit more existing cases.
Bumped up year version.
Renamed flag.
Made it possible to use standalone dataFilter.
Fixed spaces parsing in string based config.
Added support for '*' in elements list.
Be tolerant for spaces in string based config.
Useful tool methods.
Implemented dataFilter#test.
Do not modify rules when optimizing them.