DCN for the new Dataset

1. It will determine which 'DatabaseAccessor' to use from your 'database
name' input.
2. For gnome dataset, the database name must be "gnome_msr2009". For
github dataset, the database name must be "github_msr2014". Not case
sensitive for both case.
3. The file name must be 'product-names.csv'
4. Even though other options are shown, only the DCN works for the
github dataset for now.