Update and rename main.js to main.user.js

[20excal07]

• Major code cleanup to get rid of all duplicate code
• Support for timestamp tags
• Remove iframe when navigating away from a "watch" page to stop it from continuing to play in the background
• Bring iframe to frontmost layer to prevent it from being buried when switching between theater/default mode
• Attempt to hide YouTube logo in iframe
• renamed to use ".user.js" extension - if you put a link to this on the Readme, it'll automatically trigger Tampermonkey to install the script when clicked.