Enable display of a 'main page' for a group, based on some common names like Overview, Main, README, etc. Also break some of the common formatting out of the wiki I've been working on and put them into a new common file called wikiMain.css to be included with the freeki server jar. Add support for page query parameters to the groovy template handling so we can avoid re-rendering the page wrapper around content that will be embedded via javascript (for viewing main page of a group).