Adding tests for SVG components

Jest/enzyme/jsdom is kicking out some nastly looking messages because it
doesn't recognize various SVG elements, but they appear to be harmless.

src/__mocks__/SVGElement.js

@@ -0,0 +1,15 @@
+import React from 'react';
+
+import Base from 'components/SVG/Base';
+
+class SVGElement extends Base {
+  reflow() {
+    return this.setBBox(this.props.bbox);
+  }
+
+  render() {
+    return <text>Mock content</text>;
+  }
+}
+
+export default SVGElement;