Add an option to list all available types of the platform in the type selection dialog

[ylussaud]

When selecting a type for a variable of a template, at the moment only types available to the template are listed (from the list of nsURIs imported by the template). A checkbox could be added to allow the listing of all available types in the platform.
When selected, the list of all types is shown and is the nsURIs of the selected types are not already imported, they are imported automatically.