Fixes to drag-and-drop uploader

Added trailing slash to site_path to fix drag-and-drop file path as per
#446

Moved zepto.js from footer.php to header.php to load before used in
add.php and edit.php as per #491

Closed unclosed paragraph tag in edit.php
Merge pull request #495 from misterjrtaylor/1.0-dev

Fixes to drag-and-drop uploader