Set table names manually rather than using prefix.

The table_prefix method is really unreliable, as it seems to not
get loaded in a variety of confusing and annoying circumstances.
We can get around that by just specifically setting the table_name
in all of our models.
Fix the translation lookup keys for dataset creation.
Fix the background color on form elements.

Too many of the form elements looked disabled all the time; fix
that by brightening them up.
Remove extra load line from db/seeds.
Add ngram support to the UI (#24).