GUI2/Addon List: restored extra version display for upgradable or out…

…dated addons

The old GUI1 addon manager displayed both local and published versions of the addon directly in the list
if the addon was upgradable or outdated on the server. It seems to have gotten lost in the transition, so
this restores it.

data/gui/widget/addon_list.cfg

@@ -259,6 +259,7 @@
 			id = "version"
 			definition = "default_small"
 			linked_group = "version"
+			use_markup = true
 			characters_per_line = 10
 			wrap = true
 		[/label]

src/gui/widgets/addon_list.cpp

@@ -151,7 +151,24 @@ void addon_list::set_addons(const addons_list& addons)
 		item["label"] = describe_status(tracking_info);
 		data.emplace("installation_status", item);
 
-		item["label"] = addon.version.str();
+		// If the addon is upgradable or ourdated on server, we display the two relevant
+		// versions directly in the list for convenience.
+		const bool special_version_display =
+			tracking_info.state == ADDON_INSTALLED_UPGRADABLE ||
+			tracking_info.state == ADDON_INSTALLED_OUTDATED;
+
+		std::ostringstream ss;
+		if(special_version_display) {
+			ss << tracking_info.installed_version.str() << "\n";
+		}
+
+		ss << addon.version.str();
+
+		if(special_version_display) {
+			ss.str(colorify_addon_state_string(ss.str(), tracking_info.state, false));
+		}
+
+		item["label"] = ss.str();
 		data.emplace("version", item);
 
 		item["label"] = addon.author;