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.
Yeah, the insert or update thing is desirable, but like `save` (as opposed to `save!`), it will pass over a validation failure without complaining.  It expects you do care about the return value, e.g.

```ruby
some_foo = Foo.find_or_create_by(bar: 'baz')
if some_foo
  # do stuff with 
else
  tell_the_user("Sorry, buddy.  I couldn't find or create that foo you were talking about.")
end
```

If you want it to fail noisily in case it can't create the thing (I'm suggesting that in this case we do), you can use `find_or_create_by!`.

Here's the relevant documentation.  I should have linked this originally.

[`find_or_create_by`](http://apidock.com/rails/v4.0.2/ActiveRecord/Relation/find_or_create_by)

[`find_or_create_by!`](http://apidock.com/rails/v4.0.2/ActiveRecord/Relation/find_or_create_by%21)