Modpack Update Checker

There were major internal changes with this version, and any bugs will be quickly resolved.

• A JSON based config has been added, replacing the old modpack-update-checker.txt file. Old configs still work, and will NOT be migrated as of 0.6.0.
• EarlyLoader disabled, security risk.
• The JAR is now signed!

• Fixed issue with keyboard navigation the info and changelog screens in modern Minecraft versions
• Fixed update available toast appearing unconditionally
• The toast that shows up after a hotfix is completed no longer appears if 0 hotfixes are selected
• There is now an overlay in the hotfix screen that communicates that the hotfix screen cannot be closed during a hotfix