Updated data seeding script to reflect current database schema (resubmitted due to user error!)

As a new contributor I followed the steps in the Contributing.md file but received errors while running the DefaultData.sql.txt script. 

The errors were due to a new field <code>PersonIsCheckedIn</code> on the <code>Commitment</code> table which was defined as <code>Not Nullable</code> but was not being populated by the script.

I've updated the script to set this flag to 'true' in all instances.

There is another new <code>int</code> field on the <code>Commitment</code> table, <code>Status</code>, but this will default to 0 so no additional data is required for the script to run successfully.