First pass at correct Cache-Control headers & asset management

issue #932

- sets cache control headers on all routes, including 404
- is a bit aggressive in places
- handles outputting assets for the admin and theme which have a version query string
Custom connect slashes with cache headers
Updating casper
Add theme check
No first run message
Various bug fixes

- signup fix from https://github.com/TryGhost/Ghost/commit/6a5e399
- server.js error handling fix from  https://github.com/sebgie/Ghost/commit/639c0d0627b30810437904dea6ec28fa54b0bb72