Add a command for changing the acceptable versions (#206)

* feat: add packwiz settings command to allow for changing acceptable versions

* Add deduping on the list

* Fix typo in comment

* Detect out of order list and give the user an option to correct it

* Support adding and removing specific versions

* Ensure the options aren't nil

* Clean up the slice removal boilerplate

* Fix usage of slices.Delete

settings/settings.go

@@ -0,0 +1,16 @@
+package settings
+
+import (
+	"github.com/packwiz/packwiz/cmd"
+	"github.com/spf13/cobra"
+)
+
+// settingsCmd represents the base command when called without any subcommands
+var settingsCmd = &cobra.Command{
+	Use:   "settings",
+	Short: "Manage pack settings",
+}
+
+func init() {
+	cmd.Add(settingsCmd)
+}