GCode generator and unittests

closes #35

pcbdevice/models/Coordinates.py

@@ -0,0 +1,19 @@
+class Coordinate:
+	_x = -1
+	_y = -1
+	
+	def __init__(self, x = -1, y = -1):
+		self._x = x
+		self._y = y
+	
+	def setX(self, x):
+		self._x = x
+		
+	def setY(self, y):
+		self._y = y
+		
+	def getX(self):
+		return self._x
+	
+	def getY(self):
+		return self._y