Adding 404 and privacy policy pages

src/pages/404.js

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+import React from 'react';
+
+import Layout from 'components/Layout';
+import Message from 'components/Message';
+
+const ErrorPage = () => <Layout title="Page Not Found">
+  <Message type="error" heading="404 Page Not Found">
+    <p>The page you have requrested could not be found.</p>
+  </Message>
+</Layout>;
+
+export default ErrorPage;

src/pages/privacy.js

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+import React from 'react';
+
+import Layout from 'components/Layout';
+import Message from 'components/Message';
+
+const PrivacyPage = () => <Layout title="Privacy Policy">
+  <Message type="info" heading="Privacy Policy">
+    <p>Regexper and the tools used to create it are all open source. If you are concerned that the JavaScript being delivered is in any way malicious, please inspect the source in the <a href="https://gitlab.com/javallone/regexper-static" rel="external noopener noreferrer" target="_blank">GitLab repository</a>.</p>
+    <p>There are two data collection tools integrated in the app. These tools are not used to collect personal information:</p>
+    <ul>
+      <li><b>Google Analytics</b> is used to track browser usage data and application performance.</li>
+      <li><b>Sentry.io</b> is a tool used to capture and report client-side JavaScript errors.</li>
+    </ul>
+    <p>Regexper honors the browser <b>&ldquo;Do Not Track&rdquo;</b> setting and will not enable these data collection tools if that setting is enabled. Also, most popular ad blockers will prevent these tools from sending any tracking data. Disabling or blocking these data collection tools will <b>not</b> impact the performance of this app. The information collected by these tools is used to monitor application performance, determine browser support, and collect error reports.</p>
+    <p>Regexper is not supported by ad revenue or sales of any kind.</p>
+  </Message>
+</Layout>;
+
+export default PrivacyPage;