Add a rake task to import public bodies from a CSV file

For importing a very large number of public bodies, it's mostly likely
less frustrating to import them from the CSV file using this rake task
instead of using the form in the admin interface.

Fixes #1132
Make sure that the temporary file is closed before reading from it

Thanks to Louise Crow for pointing out this problem.
Remove the confusing "time remaining" message

The time estimates were confusing on two counts:

 - The messages mixed locales

 - The estimates were hugely inaccurate, since the import slows
   down as time goes on
Merge remote-tracking branch 'origin/command-line-csv-import' into rails-3-develop