Update attributes in createTable.sql

Unique was previously used in the specific_location CREATE table query on
the genloc_OSU_id attribute.  This was wrong.  In this table, artwork_id
should be unique, since each artwork can only have one location, but a
general location could have more than one artwork.  Therefore, it should
not be unique.  This commit updates removes the incorrect unique.

A timestamp was not previously included in the artwork_artist CREATE table
query.  This attribute is now included, since there are fields other than
FKs that could be updated manually.

date_create attribute in the artwork_artist CREATE table query was changed
to artwork_artist_date_created to match the Database Schema.