Show correct status when manifest permission has been removed

[fregante]

• Closes https://github.com/fregante/webext-permission-toggle/issues/39

cc @aspiers

Default (unchanged)

Manifest granted access to the GitHub.com domain; the toggle is disabled

Manifest permission removed (old behavior)

The toggle was checked and disabled even when the user removed access to the extension.

Manifest permission removed (this PR)

The toggle is unchecked and enabled if the user removed access. This reflects reality and gives the user an easy way to restore the permission.

Known bugs

• The toggle stays temporarily active/clickable after restoring the permission, but the browser doesn't let you call permission.remove() on that, so the user gets: Error: You cannot remove required permissions. 🤷‍♂️
• https://github.com/fregante/webext-permission-toggle/issues/36

[fregante]

I really wish the browser would enable their own toggle so we didn't have to use this package at all. The UI is there, but disabled. 😒 "x.com" should be clickable, but isn't.

[aspiers]

Nice work, thanks!