Avoid duplicate entries in menu

[marcocarnazzo]

If you have the same image for many smiley (i. e. ':)' and ':-)'), emoji-menu has duplicate entries.

To avoid this, I changed your code.
Here if you want to integrate this feature:

        var filenames = [];
        for (var key in options) {
            if (options.hasOwnProperty(key)) {
                var filename = options[key];
                var alreadyExists = ($.inArray(filename, filenames) > -1);
                if (!alreadyExists) {
                    filenames.push(filename);
                    html.push('<a href="javascript:void(0)" title="' + util.htmlEntities(key) + '">' + EmojiArea.createIcon(key) + '<span class="label">' + util.htmlEntities(key) + '</span></a>');
                }
            }
        }

[marcocarnazzo]

Uh, just a note.
This makes sense only with another piece: I'm trying to implement also live rendering (issue #3 )