Test that saving an existing data-set doesn't change its name
Saving an existing data-set no longer changes its name

We have older data-sets with names that don't follow the datagroup_datatype naming convention, and their names must not change when they're saved. Only new data-sets should have their names set on save.
Merge pull request #164 from alphagov/modify-doesnt-change-name

Saving an existing data-set no longer changes its name