Add GUT (CLI only) and remove gd-plug

Commit GUT directly to the git repo and remove gd-plug as it is no
longer required to install GUT.

Modify GUT to be used by command-line only.

For example:
```
cp test/.gutconfig.ci.json .gutconfig.json
godot --no-window -s addons/gut/gut_cmdln.gd
```

addons/gut/parameter_handler.gd

@@ -0,0 +1,44 @@
+var _utils = load("res://addons/gut/utils.gd").get_instance()
+var _params = null
+var _call_count = 0
+var _logger = null
+
+
+func _init(params = null):
+	_params = params
+	_logger = _utils.get_logger()
+	if typeof(_params) != TYPE_ARRAY:
+		_logger.error("You must pass an array to parameter_handler constructor.")
+		_params = null
+
+
+func next_parameters():
+	_call_count += 1
+	return _params[_call_count - 1]
+
+
+func get_current_parameters():
+	return _params[_call_count]
+
+
+func is_done():
+	var done = true
+	if _params != null:
+		done = _call_count == _params.size()
+	return done
+
+
+func get_logger():
+	return _logger
+
+
+func set_logger(logger):
+	_logger = logger
+
+
+func get_call_count():
+	return _call_count
+
+
+func get_parameter_count():
+	return _params.size()