Assegnate 5 su 5 stelle

The current add-on doesn't work in TB 68 but don't lose hope.

See this pull request "Thunderbird 68 compatibility" https://github.com/ingomueller-net/ThunderBirthDay/pull/11

I've installed this pending merge in TB 68.1.2 and it works as expected. Hopefully it will be merged, released & approved soon!