Import/Export CSV

Might need to add the ability to import CSV files, depending on whether they've already used Excel to make their inventory.
When you don't expect validation errors, prefer `save!`, which will raise an exception if it can't be saved for some reason.  `save` just returns false if it can't save, and since you're not checking the return value, it would fail silently.

`save`  is good in controllers when you're doing something like

```ruby
if @thing.save
  render 'some_kind_of_success'
else
  render 'some_kind_of_failure'
end
```