Start work on xls export

- set up to_xls method on User class
- set up route and admin controller method
- register mime type with the application
- require csv in application.rb
Merge branch 'master' of https://github.com/tmcyf/tmcyf into xls-export
Merge branch 'removed-retreat-type' of https://github.com/tmcyf/tmcyf into xls-export
XLS export working
Added admin link to users database
Merge pull request #85 from tmcyf/xls-export

Start work on xls export