Use type_to_sql in create_table & TIMESTAMP for dates

Without this change it's not possible to create a table from an ActiveRecord migration if it contains a date field.
type_to_sql converts type names used by ActiveRecord to the ones used by the database (using native_database_types). For example, BigQuery uses TIMESTAMP to store time, so ":date" has to be converted to TIMESTAMP before the table is created (and this is another thing that this change does).