Improve First Use and Uninstall Flow

[ShikenNuggets]

When you open the advanced launcher for the first time, it replaces your existing config files. Outright replacing the old files and your existing changes to them at all kinda sucks honestly, but I can see how that's somewhat necessary with how it currently works. My problem is that it does this automatically, it doesn't warn you that it's going to do this, and there's no built-in way to undo the changes. If you're aware of this before you use it then it's mostly fine, but if you aren't, and later you decide to stop using the advanced launcher, it's a bit of a pain to get back to where you were before. Was trying to walk someone through getting back to vanilla earlier and they ended up just nuking everything, which is far from ideal.

My suggestion;

• Inform the user of exactly what is going to happen when they open the launcher the first time, and get their confirmation before doing it
• Have the tool create config file backups automatically (or at the very least tell the user what files they should back up manually)
• Create a proper uninstall flow that reverts everything to those backups