add Horizontal and Vertical constraint classes

Horizontal.py

@@ -0,0 +1,6 @@
+
+from Constraint import Constraint
+
+class Horizontal(Constraint):
+    def __init__(self, shape):
+        self.shape = shape

Vertical.py

@@ -0,0 +1,6 @@
+
+from Constraint import Constraint
+
+class Vertical(Constraint):
+    def __init__(self, shape):
+        self.shape = shape