Make import look in more places for packs

Now supports Curse/Twitch instance names
and folders containing minecraftinstance.json or manifest.json

curseforge/cursedir_other.go

@@ -0,0 +1,10 @@
+// +build !windows
+
+package curseforge
+
+import "errors"
+
+// Stub version, so that getCurseDir exists
+func getCurseDir() (string, error) {
+	return "", errors.New("not compiled for windows")
+}