Fixed issue when quantity is 0
Upgraded ember-cli-sass to not produce sourcemaps

Don’t produce source maps in production
Fixes #17

There were a couple of issues:
1) Validation was wrong on adjust inventory items, allowing users to
remove more than the available items
2) Inventory locations being deleted turns out to be a bad thing
because they are needed for historical purposes
3) When adjusting an item to add inventory, the data was not properly
being saved.