Add Project Wikis to Sloecode

We want to allow projects to have wikis for project documentation. To this end we want to integrate wikkid (http://launchpad.net/wikkid) into sloecode. The basic idea is that if enabled, user swill be able to navigate to a '/wiki/' URL for any project and we'll serve the project wiki content.

Wiki content will be stored in a special 'wiki' branch that is automatically created for each project when the project is registered.