Table.description_field should be done dynamically #17

The description field (shown inside of comboboxes for example) is stored inside of the Table. It is set once on Table creation via add_table, or Database.auto_add_tables.

It presents a problem on dynamic queries, as the field name may not yet be known until the dynamic query occurs.

We need to either make description_field a property or a method, which dynamically returns the field ('name' if it exists, or 2nd column). This should fix issues where dynamic queries are concerned.