Fix conversion of epub2/ncx TOCs to <ol> form

[chine]

Re: Issue 97

[rkwright]

Defer for now. It targets master and we need a reproducible case.

[danielweck]

This PR indeed targets the master branch instead of develop. Furthermore, the file epub-modules/epub/src/models/package_document.js now resides at js/epub-model/package_document.js (since a significant refactoring).
However, the fix itself is obviously still valid, and should be reviewed appropriately.
Here is a direct link to the new code location:
https://github.com/readium/readium-js/blob/master/js/epub-model/package_document.js#L178

        // Description: Constructs an html representation of NCX navPoints, based on an object of navPoint information
        // Rationale: This is a recursive method, as NCX navPoint elements can nest 0 or more of themselves as children
        function addNavPointElements($navPointDOM, $ol) {

            // Add the current navPoint element to the TOC html
            var navText = $navPointDOM.children("navLabel").text().trim();
            var navHref = $navPointDOM.children("content").attr("src");
            var $navPointLi = $('<li class="nav-elem"></li>').append(
                $('<a></a>', { href: navHref, text: navText })
            );

            // Append nav point info
            $ol.append($navPointLi);

            // Append ordered list of nav points
            if ($navPointDOM.children("navPoint").length > 0 ) {

                var $newLi = $("<li></li>");
                var $newOl = $("<ol></ol>");
                $.each($navPointDOM.children("navPoint"), function (navIndex, navPoint) {
                    $newOl.append(addNavPointElements($(navPoint), $newOl));
                });

                $newLi.append($newOl);
                $ol.append($newLi);
            }
        }