Fixed bug

Fixed a bug where attempting to call `html5_qrcode()` on an element not yet attached to the DOM causes video and canvas to resolve to undefined.
Changing jQuery extension methodology

Modified the way jQuery is extended to fit better with best practices.

Also, now that the code is using jQuery objects to find the elements rather than selectors, the elements no longer need IDs. This is peferred, so as to prevent accidental name conflicts.
Merge pull request #11 from cyborgx37/master

Better adherence to best practices