Added optional notifications for watched trees changing status.
(Due to a bug in Firefox this has temporarily necessitated opening the options page in its own tab instead of inside about:addons
https://bugzilla.mozilla.org/show_bug.cgi?id=1382953)

Prevented possibility of user-fingerprinting during status requests via leak of extension UUID in Origin header.
(https://bugzilla.mozilla.org/show_bug.cgi?id=1257989)

Improved keyboard accessibility in options page and the popup.