(Settings) - Configured "interactive" checkbox behaviour

- Added event handler for "interactive" checkbox to handle showing and hiding "scrollbars" checkbox
- Moved custom in-page CSS styles below linked stylesheets to properly override styles from bootstrap, etc
- Added custom styles to indent "scrollbars" checkbox and bold "interactive" checkbox label
- Removed unnecessary .form-group class from "zoom" select
- Removed disabled attr from "scrollbars" checkbox