Gadgets feature list does not traverse dependencies

When the list of gadget features is processed, only features that are required directly from the module prefs are taken into account - the dependency tree is not traversed.

This will cause an issue for the following example:

• MyGadget requires myCustomFeature.
• myCustomFeature requires pubsub-2 as a dependency.
• pubsub-2 is not added the MyGadget's features list
• When the container checks has_feature('pubsub-2'), it will return false
• The gadget does not properly implement pubsub-2.