significantly refactor presentational components

src/components/presentational/Timeline/Markers.js

@@ -0,0 +1,31 @@
+import React from 'react';
+
+const TimelineMarkers = ({ getEventX, getCategoryY, transitionDuration, selected }) => {
+  function renderMarker(event) {
+    return (
+      <circle
+        className="timeline-marker"
+        cx={0}
+        cy={0}
+        style={{
+          'transform': `translate(${getEventX(event)}px, ${getCategoryY(event.category)}px)`,
+          '-webkit-transition': `transform ${transitionDuration / 1000}s ease`,
+          '-moz-transition': 'none',
+          'opacity': 0.9
+        }}
+        r="10"
+      >
+      </circle>
+    )
+  }
+
+  return (
+    <g
+      clipPath={"url(#clip)"}
+    >
+      {selected.map(event => renderMarker(event))}
+    </g>
+  );
+}
+
+export default TimelineMarkers;