Handle `dev:prime` seeds in convetional file

Rails' convention is to do DB seeding in `db/seeds.rb`. This moves the logic
from the `.rake` file to the `.rb` file.

It has the nice side-effect of being called via `rake db:seed`, in addition to
`rake dev:prime`.

Also, is allows for calls to `FactoryGirl` to be fully out-dented and not
crammed inside of nested blocks.
This doesn't seem to do the trick. Is it not overwriting?

I also tried with

```
remove_file "db/seeds.rb"
copy_file "seeds_file.rb", "db/seeds.rb"
```

but got the same failure