addon/state: Add addons_tracking_list typedef

So I don't need to keep repeating the same std::map template
instantiation all over the place.
gui2/taddon_description: Refactor add-on name coloring logic
gui2/taddon_description: Add a row for listing add-on dependencies
gui2/taddon_description: Implement listing of add-on dependencies

This requires passing additional information about available add-ons (on
the server) and installed add-ons to the dialog's constructor. The
dependency list is a completely flat label displaying a comma-separated
list, with color-keyed installation statuses like the Status field and
the main add-ons list display.