created PlaneTracker (int plane_tracker.py), which implements multitarget planar tracking

rewritten feature_homography.py using it
added plane_ar.py - simple augmented reality sample

samples/python2/common.py

@@ -204,3 +204,9 @@ def getsize(img):
 
 def mdot(*args):
     return reduce(np.dot, args)
+
+def draw_keypoints(vis, keypoints, color = (0, 255, 255)):
+    for kp in keypoints:
+            x, y = kp.pt
+            cv2.circle(vis, (int(x), int(y)), 2, color)
+