Prepare CatalogComponent to be sub-classed.

1. Make private members protected.

2. Make loadData() and selected() virtual

3. Add a parameter to the constructor that enables / disables the
   calling of loadData() at construct time.

4. Make loadData() a proxy for a protected method _loadData( bool )
   that actually loads the data.

5. Make provisions for having "fake" catalogs, where the catalog name
   and ID are not official and should not be used as names.