significantly refactor presentational components

src/components/presentational/Timeline/DatetimeDot.js

@@ -0,0 +1,28 @@
+import React from 'react'
+
+export default ({
+  category,
+  events,
+  x,
+  y,
+  onSelect,
+  styleProps,
+  extraRender
+}) => (
+  <g
+    className='datetime'
+    transform={`translate(${x}, ${y})`}
+    onClick={() => onSelect(events)}
+  >
+    <circle
+      className="event"
+      cx={0}
+      cy={0}
+      style={styleProps}
+      r={5}
+    >
+    </circle>
+    { extraRender ? extraRender() : null }
+  </g>
+)
+