Fix for changes in Firefox 72 proxy API

Switched to the new preferences API. Configuration adjustments are needed as the extension now just toggles between enabling or disabling a given Proxy type. All settings are now set in the normal firefox proxy settings. This allows setting every kind of proxy setting Firefox supports, instead of the just the subset the extension was exposing.

Save the proxy ON/OFF state and restore in on startup

Fix broken default options and require one less permission (access to tabs)

Add-on ID is now set in the manifest to avoid issues with storage API