Created a CSV controller concern.  Currently it just works to download CSV
files, but the code from the Exzweight machine might be able to be modified
and placed there.

The CSV download works, but leaves csv files in the public folder.  These
files should be temporary, and thus may also warrant moving to the tmp
folder.

 On branch experimental
 Changes to be committed:
	new file:   app/controllers/concerns/csv_methods.rb
	modified:   app/controllers/machines_controller.rb
	modified:   app/models/exzweight.rb
	modified:   app/models/machine.rb
	modified:   app/views/machines/index.html.erb
	modified:   config/routes.rb