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/input_factory.gd

@@ -0,0 +1,140 @@
+# ##############################################################################
+#(G)odot (U)nit (T)est class
+#
+# ##############################################################################
+# The MIT License (MIT)
+# =====================
+#
+# Copyright (c) 2020 Tom "Butch" Wesley
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in
+# all copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+# THE SOFTWARE.
+#
+# ##############################################################################
+# Description
+# -----------
+# ##############################################################################
+
+# Implemented InputEvent* convenience methods
+# 	InputEventAction
+# 	InputEventKey
+# 	InputEventMouseButton
+# 	InputEventMouseMotion
+
+# Yet to implement InputEvents
+# 	InputEventJoypadButton
+# 	InputEventJoypadMotion
+# 	InputEventMagnifyGesture
+# 	InputEventMIDI
+# 	InputEventPanGesture
+# 	InputEventScreenDrag
+# 	InputEventScreenTouch
+
+static func _to_scancode(which):
+	var key_code = which
+	if typeof(key_code) == TYPE_STRING:
+		key_code = key_code.to_upper().to_ascii()[0]
+	return key_code
+
+
+static func new_mouse_button_event(position, global_position, pressed, button_index):
+	var event = InputEventMouseButton.new()
+	event.position = position
+	if global_position != null:
+		event.global_position = global_position
+	event.pressed = pressed
+	event.button_index = button_index
+
+	return event
+
+
+static func key_up(which):
+	var event = InputEventKey.new()
+	event.scancode = _to_scancode(which)
+	event.pressed = false
+	return event
+
+
+static func key_down(which):
+	var event = InputEventKey.new()
+	event.scancode = _to_scancode(which)
+	event.pressed = true
+	return event
+
+
+static func action_up(which, strength = 1.0):
+	var event = InputEventAction.new()
+	event.action = which
+	event.strength = strength
+	return event
+
+
+static func action_down(which, strength = 1.0):
+	var event = InputEventAction.new()
+	event.action = which
+	event.strength = strength
+	event.pressed = true
+	return event
+
+
+static func mouse_left_button_down(position, global_position = null):
+	var event = new_mouse_button_event(position, global_position, true, BUTTON_LEFT)
+	return event
+
+
+static func mouse_left_button_up(position, global_position = null):
+	var event = new_mouse_button_event(position, global_position, false, BUTTON_LEFT)
+	return event
+
+
+static func mouse_double_click(position, global_position = null):
+	var event = new_mouse_button_event(position, global_position, false, BUTTON_LEFT)
+	event.doubleclick = true
+	return event
+
+
+static func mouse_right_button_down(position, global_position = null):
+	var event = new_mouse_button_event(position, global_position, true, BUTTON_RIGHT)
+	return event
+
+
+static func mouse_right_button_up(position, global_position = null):
+	var event = new_mouse_button_event(position, global_position, false, BUTTON_RIGHT)
+	return event
+
+
+static func mouse_motion(position, global_position = null):
+	var event = InputEventMouseMotion.new()
+	event.position = position
+	if global_position != null:
+		event.global_position = global_position
+	return event
+
+
+static func mouse_relative_motion(offset, last_motion_event = null, speed = Vector2(0, 0)):
+	var event = null
+	if last_motion_event == null:
+		event = mouse_motion(offset)
+		event.speed = speed
+	else:
+		event = last_motion_event.duplicate()
+		event.position += offset
+		event.global_position += offset
+		event.relative = offset
+		event.speed = speed
+	return event