[FEATURE] RTE: Keep HTML5 block tags when clean pasting text

[FEATURE] RTE: Keep HTML5 block tags when clean pasting text

Description: When pasting while pasteStructure or pasteFormat behaviour
is enabled, the default behaviour should keep HTML5 block tags article,
aside, footer, header, nav and section. These defaults may be modified
in Page TSConfig with buttons.pastebehaviour.[behaviour].keepTags.

Change-Id: I448b7c5e3dd73eeb037aba805406f429bb93461a
Releases: 6.0
Resolves:#38683
Reviewed-on: http://review.typo3.org/12638
Reviewed-by: Stanislas Rolland
Tested-by: Stanislas Rolland