Top level element should be separated by 2 new lines in the XWiki Syntax renderer

This is because wikimodel doesn't generate events for 1 or 2 new lines between top level elements. They are not considered semantic by wikimodel. So there isn't much we can do.

For ex this means that the following:

para
----
para

will get transformed to:

para

----

para

if the user switches to the wysiwyg and back to the wiki editor. This is acceptable IMO since it simply means we're cleaning the content. Same as with "** something"" which we transform into "*something*".

In the future it would be good to "clean" the document content when in the wiki editor and when the user saves the content.