categories

@georgetmayorga @cgruppioni 
We need the every row in category to be a unique combination. So we need to add a migration for 
<code>add_index :categories, [:name, location_id], unique: true.

We also DON'T want <code>unique: true</code> for the index on categories by itself. We want to be able to have "Music" multiple times as long as the location_id name pair is different