Add some install* / uninstall* scripts

Scripts/uninstall-git-extensions.ps1

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+<#
+.SYNOPSIS
+	Uninstalls Git Extensions
+.DESCRIPTION
+	This PowerShell script uninstalls Git Extensions from the local computer.
+.EXAMPLE
+	PS> ./uninstall-git-extensions
+.LINK
+	https://github.com/fleschutz/PowerShell
+.NOTES
+	Author: Markus Fleschutz | License: CC0
+#>
+
+try {
+	"Uninstalling Git Extensions, please wait..."
+
+	& winget uninstall --id GitExtensionsTeam.GitExtensions
+	if ($lastExitCode -ne "0") { throw "Can't uninstall Git Extensions, is it installed?" }
+
+	"Git Extensions is uninstalled now."
+	exit 0 # success
+} catch {
+	"Sorry: $($Error[0])"
+	exit 1
+}