Add pack update checker

* Upgradle
* Update Forge
* Increase version
* Fix inversion of disableGuiAfterFirstLaunch
* Add optional pack update checker.
* Notifies users if the pack version set in the config is not the same
as the pack version found on a hosted file.
* File should be a single line with just the version using a *.txt
extension. Example can be found
[here](https://raw.githubusercontent.com/TehNut/LaunchGui/1.7.10/version.txt)