Allow options to be bound to a keyboard shortcut

Remove jQuery

It is not as useful these days with modern browser APIs.
Besides, keeping it up-to-date has always been a chore.

Improve diagnostics when loading/saving data

  - Show errors if the saving or loading fails for any reason.
  - Display a warning if the data gets changed elsewhere.
  - Throttle save rate slightly to avoid exhausting the quota too fast.

Minor improvements

  - Slightly improve appearance of Options UI
  - Silence errors that occurred when adding CSS to forbidden areas.
  - Move jQuery out of the repo.
  - Update jQuery and LICENSE.

Add more descriptive title for Options

Provide better error messages from user script

Initial commit