Added idle timer logic.
Adding roadmap.
Adding options page, with configurable idle timer.

- Borrowing pieces of an extension config page from another project, so
  there's some commented-out HTML for sound config to undummy later.
- Added jQuery UI and "Cupertino" theme.
- Content script now uses configured idle time.
Forgot to update roadmap.
Fixed obsessive idle timer resetting.

The script fires mousemove events every time a message comes in it
seems, so I threw in some checks to only update on mousemove when the
mouse has actually moved.