Add drag and drop to the Spline UI

Move event handling for the field widget into Field

Signed-off-by: Ravago Jones <ravagojones@gmail.com>
Change-Id: Id566b7a549fb568a089f50eae6d5d2b483a615ee
diff --git a/frc971/control_loops/python/graph.py b/frc971/control_loops/python/graph.py
index 1b83713..456edd1 100644
--- a/frc971/control_loops/python/graph.py
+++ b/frc971/control_loops/python/graph.py
@@ -53,3 +53,5 @@
         # renumber the x-axis to include the last point,
         # the total time to drive the spline
         self.axis.xaxis.set_ticks(np.linspace(0, total_time, num=8))
+
+        self.queue_draw()