Add created_date and updated_date fields to all tables

[Barry van Oudtshoorn]

I was just asked to produce a report showing which songs have been added to OpenLP in the past six months. Unfortunately, however, there's no easy way to do this, as the data simply isn't available in the database. What I would propose is the addition of two fields to most (all?) tables in the "songs" db, to track the timestamps for insertion and last update.

Yes, there is the "songusage" database, but that solves a slightly different problem, although admittedly with some cross-over. (I was able to get useful data out of it to satisfy the request.)