Add HTML details test to extended descriptions test book

[avneeshsingh]

HTML details is getting good adoption in the industry. It works very well with scrolling view, as it is designed keeping in mind the web. But many reading systems customize the view and make it appear like a paginated view of the book. In such views, HTML details with good amount of text cause visual disruptions.

Therefore this test should be added to the extended descriptions test book on epubtest.org. This test is already in experimental test book, and can be copied from it.

[avneeshsingh]

The smaller extended description test book on epubtest.org has test for HTML summary. We mainly need to increase the text contained in the HTML details element so that it overflow to the next paginated view.