Rename FrameSequencer to FrameGrabber and break out into separate file.

Add a test case that the bmp2dhr output of input filenames containing
'.'  are handled correctly.

Break out video.Mode into video_mode.VideoMode to resolve circular
dependency.

transcoder/frame_grabber_test.py

@@ -0,0 +1,25 @@
+import unittest
+
+import frame_grabber
+
+
+class TestFileFrameGrabber(unittest.TestCase):
+    def test_output_dir(self):
+        self.assertEqual(
+            "/foo/bar",
+            frame_grabber.FileFrameGrabber._output_dir("/foo/bar.mp4")
+        )
+
+        self.assertEqual(
+            "/foo/bar.blee",
+            frame_grabber.FileFrameGrabber._output_dir("/foo/bar.blee.mp4")
+        )
+
+        self.assertEqual(
+            "/foo/bar blee",
+            frame_grabber.FileFrameGrabber._output_dir("/foo/bar blee.mp4")
+        )
+
+
+if __name__ == '__main__':
+    unittest.main()