retrieve most recent release from Heroku, and show it in the footer

Puts a link into the footer, so you can see the current release.  Closes #261

@megamattron You will need to add a few new config variables to get this to work.

`HEROKU_EMAIL` --> The email address you registered the pullup app under
`HEROKU_AUTH_TOKEN` --> on the command line, run `heroku auth:token` to receive your token
`HEROKU_APP` --> Name of the pullup app