Added URL submission form for web.py

Asked about this in the IRC channel earlier today and was told web.py was basically deprecated since the next release will be more like malwr.com... but in the interim these changes enable simple URL submission from the web interface.

Added a 'Submit URL' href to base-web which calls a simple new form, url.html, rendered by web.py. Submissions to url.html call url_success.html to display the success message and web.py simply calls db.add_url to submit.