Change category view in New Resource Dialog

[jng]

The Category view in the New Resource Dialog is a bit cumbersome as the Available Templates view will only show templates for the selected category. For example, I'd guess most users won't realise that you can create a SQLite load procedure because it's hidden in a separate category (MGOS 2.2) that most users probably won't select.

Instead the Category View should be a checked list box, with the Available Templates view being filtered on what's checked in the Category View. By default, all categories should be checked meaning all templates are visible.

[jng]

Fixed r5661 and r5662. I used ListBox with multi-select instead of CheckedListBox because CheckedListBox is a PITA to use!