Add hash to uploads table to reduce unnecessary changes

This impacts the _sparcd_db.py_ file - **get_uploads** and **save_uploads** functions, the _create_db.py_ file, and the **uploads** table in the DB

The **get_uploads** function need to return the stored hash value.
The **save_uploads** function needs to do the following:
1. generate a hash for each upload's JSON
2. compare the hash against what was returned from the database if there's a hash value
3. save/update the update into the database if the hash value is different or not found