Add game title and author to ContentDB error messages

Fixes minetest#12671

builtin/mainmenu/dlg_contentstore.lua

@@ -124,12 +124,12 @@ local function start_install(package, reason)
 
 	local function callback(result)
 		if result.msg then
-			gamedata.errormessage = result.msg
+			gamedata.errormessage = fgettext("Error downloading \"$1\": $2", package.title, result.msg)
 		else
 			local path, msg = pkgmgr.install_dir(package.type, result.path, package.name, package.path)
 			core.delete_dir(result.path)
 			if not path then
-				gamedata.errormessage = msg
+				gamedata.errormessage = fgettext("Error installing \"$1\": $2", package.title, msg)
 			else
 				core.log("action", "Installed package to " .. path)