Migrate to a UI that looks more like other software package managers, giving
more space to each addon by hiding the list when an addon is selected, and
providing a "back" button to get back.
Implements a two-style view option for the list of addons: expanded and
condensed, via a delegate that provides the drawing function for each row in
the table based on two different widget designs.
This shifts to use the model-view-controller pattern for the list of addons,
and moves to using a full model class rather than an indexed array for the
data storage and management. This enables much more information to be stored
as part of the new AddonManagerRepo data type. It now wraps the Macro class
for macros, supports Preference Packs, and provides access to the Metadata
object.
