Added Python code to create DDL SQL for SQLite

SQLite doesn't support alter table statements for creating foreign keys
so I had to add the foreign key creation statements to the table
creation statements for SQLite.  The Python code for creating the DDL
SQL scripts is now capable of creating them for MSSQL, MySQL,
PostgreSQL, and SQLite.  ODM2 for SQLite will likely be used by
HydroShare and BiG CZ.