Allow plugins to have html templates

I have another idea. This is an extension to JIRA issue JSPWIKI-859

When building plugins we can currently specify the following in jspwiki_module.xml

<?xml version="1.0" encoding="UTF-8"?>
<modules>
   <plugin class="com.digitalspider.jspwiki.plugin.ImageGalleryPlugin">
      <author>David Vittor</author>
      <minVersion>2.10.1</minVersion>
      <script>/jssor/js/jssor.slider.min.js</script>
      <stylesheet>/jssor/css/jssor.slider.css</stylesheet>
      <alias>ImageGallery</alias>
   </plugin>
</modules>

I think we should add an extra parameter here called "<template>" that will provide access to a html template for the plugin to render.

At the moment I'm thinking a "Freemarker" template engine, but am happy to other suggestions. It would allow users to change the HTML template without necessary changing the code in the plugin.

Then in the plugin it would finish with:

• return render(template, params);