Sort messages from newest to oldest

My team members and I use mailcatcher heavily, and we have been slightly annoyed by constantly needing to scroll to the bottom to open the latest message. This pull request sorts messages in reverse chronological order so that the most recent message is always at the top of the message list.

I have included application.js as it looks like you are checking in the result of the CoffeeScript compilation.  My version of CoffeeScript always uses braces for if blocks, so the changes to that file seem more significant than they really are.  Please let me know if you'd like me to remove that file or only include the change relevant to this pull request.