put improved foreign key constraints on DB to fix bug where when I delete a cset, that was being used to compare_to, it breaks

db.py

@@ -8,6 +8,8 @@ def connect_db(as_object):
         conn = sqlite3.connect('/data/finance.db')
     else:
         conn = sqlite3.connect('./finance.db')
+    # allow deleting cset to clear our compare_to properly in finance table
+    conn.execute("PRAGMA foreign_keys = ON;")
     if as_object:
         conn.row_factory = sqlite3.Row  # This allows us to access columns by name
     return conn