Merge pull request #74 from ehmatthes/ongoing_development

Ongoing development
Removed most view-caching code, left in calls to invalidate.
Added simple queryset cache to index page.
Removed caching of querysets; subtle effects such as more_submissions becoming stale.
Added prefetch_related('submitter') to users with show_invisible=True.
Merge pull request #75 from ehmatthes/optimize_queries

Optimize queries
Comments display clickable urls.