Added options menu so people can choose which enhancements to use

The options menu is sandwiched between the search input field and the contribute playlist button. It is styled identically to the visitor menu (opened by clicking your face).

On a high level, a cookie is set if the user chooses to disable an option, and this act is then communicated to the relevant enhancement file for processing.

I've also renamed main.js to itunes-button.js to better maintain that these files are enhancement modules.