Parsoid/HTML based LST

1-line summary: Use HTML-supported section tags with valid opening and closing tags rather than the self-closing section-tags.

Issues that need to be resolved

 * See also: Bug 69331
 * Paragraph merging across original pages: Text stored as single wiki page per original book page, with paragraphs potentially broken up. When reading, the page breaks should not be visible.
 * Transclusion is primarily by chapter (?) but there are other use case (dictionnaries...)
 * which kind of transclusion is used there? Other kinds of overlapping sections? -- probably straightforward, no mis-nesting

Example of current workflow on wikisource
Content of Page:Foo/1 Foo beginning of

Content of Page:Foo/2 paragraph

Chapter 2

Result of "" Foo

beginning of paragraph