Files db field type (task #3317)
Files db field type (task #3317)

Since we are no longer extending Related field handler in the Base
Files field handler, we need to specify the db field type using the
`DB_FIELD_TYPE` constant, which will be used by fieldToDB method
during CSV migrations.

QoboLtd/cakephp-csv-migrations,QoboLtd/cakephp-csv-migrations