Fix warning that NUll was not a valid integer value

Upon insertion, warnings would show stating that 'NULL' was not a valid
intger value for rev_parent_id. Fixed by changing the default value in
the schema from 'NULL' to None, effectively casuing the database to
populate the table with NULLS instead of inserting them. Similarly, NULL
values in the revision.csv are now replaced with None
Renamed to indicate script uses SQLAlchemy core
Renamed to indicatescript uses ORM
Added new script for MySQLdb + SQLAlchemy Core
New script to for insertions using MySQLdb+Core and renamed accordingly
Added files for PyMySQL + Python 2