Bug fix: These routines accessed the GTK app from another thread. Replacing with calls to gobject.idle_add.
Replacing SQL-generating Python code in favor of separate .sql files to make it easier to maintain the source code, document the schema and manipulate the database manually.
Bug fix: Buttons were sensitive when they should not have been. on_row_select() failed if there was no row selected.
Improving docstring and comment. Making call mechanism to parent class __init__() consistent with other calls.