preview html changes

Feature: preview Stage URLs in a new tab. 
Consists of: Small HTML/JS changes. 
Notes: 
* JS should be moved from HTML into separate file in static.
* There exists a check for "http://" because of undesired behavior where the lack thereof would result in Django directing a sample url "www.example.com" to "ab-testing-tool-server/www.example.com" instead of the desired "http://www.example.com"
Good thought. The only issue I have about the html5 help message is that it isn't helpful in indicating to a user it wants the "http://" prepended, only that "www.example.com" is not a valid URL. In any case, depending on UX input, these forms will probably be re-implemented.