Add support for generated table columns

There is this new feature called generated columns in SQLite 3.31.0. See here for details. We should add support for this in the future. As far as I can tell these parts of DB4S need to be changed:

• Parser and SQL object representation classes
• Disable writing to these columns in the Browse Data tab
• Automatically refresh contents of generated columns when other columns are changed in the Browse Data tab
• Add support for this in the Edit Table dialog

The first item is the most important one since it is required for even opening these databases.