Simplify user permissions updater rake

The earlier version pushed permission information
to applications irrespective of whether the user
has used it in the past or not.
Merge pull request #290 from alphagov/fix-user-permissions-rake

Simplify user permissions updater rake
Export user permissions and roles in CSV format.
Add rake tasks for exporting permissions and roles
Order output by user name
Merge pull request #291 from alphagov/export_user_permissions

Export user permissions
Convert rake task arguments to environment vars.

Allows for application names with spaces and is more consistent with
other tasks in the namespace.
Merge pull request #293 from alphagov/export_user_permissions

Convert rake task arguments to environment vars.