Change Details

For reading, writing, and eventually getting notified of changes to settings. Promise-based API taking into account defaults values.

For reading, writing, and eventually getting notified of changes to settings. Promise-based API taking into account defaults values. Also drop unused `loadSettings` callback in options page.

For reading, writing, and eventually getting notified of changes to settings. Promise-based API taking into account defaults values. Also drop unused `loadSettings` callback in options page.