significantly refactor presentational components

src/components/presentational/Timeline/Clip.js

@@ -0,0 +1,15 @@
+import React from 'react';
+
+const TimelineClip = ({ dims }) => (
+  <clipPath id="clip">
+    <rect
+      x={dims.margin_left}
+      y="0"
+      width={dims.width - dims.margin_left - dims.width_controls}
+      height={dims.height - 25}
+    >
+    </rect>
+  </clipPath>
+);
+
+export default TimelineClip;