GUI2/Addon List: restrict markup to name and installation status fields

We don't want markup in any of the other fields. I still need to find a slightly better solution for the name
field, though. We don't want users to be able to use markup unnecessairly, but we do need markup to highlight
the names of ready-to-upload addons.

This fixes warnings about unescaped ampersands in the Author field.

data/gui/widget/addon_list.cfg

@@ -219,6 +219,7 @@
 						linked_group = "name"
 						wrap = true
 						characters_per_line = 20
+						use_markup = true
 					[/label]
 				[/column]
 
@@ -237,6 +238,7 @@
 						id = "installation_status"
 						definition = "default_small"
 						linked_group = "name"
+						use_markup = true
 					[/label]
 				[/column]
 

src/gui/widgets/addon_list.cpp

@@ -129,8 +129,6 @@ void addon_list::set_addons(const addons_list& addons)
 		std::map<std::string, string_map> data;
 		string_map item;
 
-		item["use_markup"] = "true";
-
 		if(!tracking_info.can_publish) {
 			item["label"] = addon.display_icon();
 			data.emplace("icon", item);