Revert "LPS-50259 No need to normalize path like freemarker did, since we redo all the logic of loading a template."

This reverts commit 5c7935397e3c52fa52375442039267b1c8eaf6eb.
Fix paste HTML code in Creole Editor

On paste code to Creole editor the elements, which cannot be
handled by Creole, should be omitted. Also, on converting to
Creole the characters, which are reserved to Creole, should be
escaped.

Add headings to the list of allowed elements on paste HTML