The test page now uses prism-core.js instead of prism.js (#1908)

Instead of `prism.js`, the test page will now use `prism-core.js`. This means that Markup, CSS, C like, and JS are not included by default which will cause them to behave like any other language.

test.html

@@ -127,7 +127,7 @@ <h2>Test drive</h2>
 <footer data-src="templates/footer.html" data-type="text/html"></footer>
 
 <script src="scripts/utopia.js"></script>
-<script src="prism.js"></script>
+<script src="components/prism-core.js"></script>
 <script src="components.js"></script>
 <script src="scripts/code.js"></script>
 <script src="scripts/vendor/promise.js"></script>