Improvements to the user messages view

I revised the conversation index to show last response date and who sent
it, and added a link to easily go back to it. I also added a box for
each message so you can easily view the Markdown source of each message.
1 job for development in 10 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
canceled #217696977
rspec-integration

00:00:10