Removed double youtube CSP

Was included twice in manifest CSP. Also added preview to options,
renamed settings to display settings
Refactored unsubscribe handling

Move app code out of options
Organized app.js functions into separate libraries

Separated out polling, badge, notifications features into separate
libraries
More app.js cleanup

Moved unsubscribe to feedupdater, move fonts to frontend fonts include
Removed app.js