1) Class WheelBaseData add to act as a common resource for data classes.
   Hierarchy is now ComponentBase -> WheelBaseData -> dataclass for individual component
2) Moved some validation routines into WheelBaseData class.
3) Wheel List class which is a wrapper for QStringList and supports entry, rotor
   and reflector lists in machine table.
4) Added new validation to ensure entry, rotor or reflector wheels cannot be
   deleted if they are referenced in a machine definition on the machine table.
5) Added MySql class to interrogate MySql database information_schema to
   obtain enum values for a given schema, table and column.