Throw Error when dist generation doesn't recognize a value.

[tylerrowsell]

          missing underscores here.

Originally posted by @tylerrowsell in #349 (comment)

This should have been caught by dist generation not being able to find the attribute. We should throw an error when reading these files into the DB if an attribute can't be found.

A little more details...

When parsing the data files to load into the database, if an attribute or value is missing when referenced by a category or attribute, an error should be thrown so the user knows it failed.

[elsom25]

When parsing the data files to load into the database, if an attribute or value is missing when referenced by a category or attribute, an error should be thrown so the user knows it failed.

The seeding itself doesnt do checking for performance reasons. But the integration tests check this. We can maybe instrument our dev commands to invoke both (basically a manual seed does it; the raw seed continues to go fast)