* Remove Styx because it is not longer maintained (Tobi823/ffupdater#101).
* Improve version comparison with G00fY2/version-compare (Tobi823/ffupdater#98).
* Fix opt-out of apps from background update check ("Excluded applications") for Firefox Release, Firefox Beta and Firefox Nightly (Tobi823/ffupdater#97).
* Don't crash during app installation/update when no or only very little storage is available (Tobi823/ffupdater#96).
* When app update is unsuccessful, show more detailed error message.
* Update dependencies