Making the getHTMLBodyContents() function more robust
When displaying HTML fulltext, instead of returning the whole html
document and inserting it inside a OJS webpage in a div-tag (that will
make the page not validate), this function grabs the <body> element's
contents and wraps it in a div tag and returns that string.

This allows the HTML fulltext page in OJS validate. The returned string
conatins a html document fragment where empty tags are self-closed as in xhtml-style.