New Navigation & Pathfinding support for 2D

-Added Navigation & NavigationPolygon nodes
-Added corresponding visual editor
-New pathfinding algorithm is modern and fast!
-Similar API to 3D Pathfinding (more coherent)

demos/2d/navpoly/engine.cfg

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+[application]
+
+name="Navigation Polygon (2D)"
+main_scene="res://navigation.scn"

demos/2d/navpoly/navigation.gd

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+
+extends Navigation2D
+
+# member variables here, example:
+# var a=2
+# var b="textvar"
+var begin=Vector2()
+var end=Vector2()
+var path=[]
+
+const SPEED=200.0
+
+func _process(delta):
+
+
+	if (path.size()>1):
+	
+		var to_walk = delta*SPEED
+		while(to_walk>0 and path.size()>=2):
+			var pfrom = path[path.size()-1]
+			var pto = path[path.size()-2]
+			var d = pfrom.distance_to(pto)
+			if (d<=to_walk):
+				path.remove(path.size()-1)
+				to_walk-=d
+			else:
+				path[path.size()-1] = pfrom.linear_interpolate(pto,to_walk/d)
+				to_walk=0
+				
+		var atpos = path[path.size()-1]	
+		get_node("agent").set_pos(atpos)
+		
+		if (path.size()<2):
+			path=[]
+			set_process(false)
+				
+	else:
+		set_process(false)
+
+
+
+func _update_path():
+
+	var p = get_simple_path(begin,end,true)
+	path=Array(p) # Vector2array to complex to use, convert to regular array
+	path.invert()
+	
+	set_process(true)
+
+
+func _input(ev):
+	if (ev.type==InputEvent.MOUSE_BUTTON and ev.pressed and ev.button_index==1):
+		begin=get_node("agent").get_pos()
+		#mouse to local navigatio cooards
+		end=ev.pos - get_pos()
+		_update_path()
+
+func _ready():
+	# Initialization here
+	set_process_input(true)
+	pass
+
+