Automatic Discord install folder detection

[Speshkitty]

A short snippet that detects the highest version number in %LOCALAPPDATA%/Discord and stores it in a variable

for /f "usebackq delims=" %%i in (`
  powershell -c "ls -Name -Path "%LOCALAPPDATA%/Discord" -Filter app-* | sort { [version]($_.Name -replace '^.*-(\d+(\.\d+){1,3})$', '$1') } -Descending | select -Index 0;"
`) do set folder=%%i

This uses System.Version for comparison, so should avoid any weird sorting issues.

I'm not sure what the best way to work that into the existing install script is, which is why this is an issue and not a PR.

[Maverynthia]

The install script is just a .bat file. So maybe just do all of it in a powershell script?