[nextgen/cardstack] big improvements

- Implement return types
- page numbers
- better subpage resolve delay
- error handling and system error cards
- code cleanup

labscore/utils/embed.js

@@ -148,6 +148,12 @@ module.exports.createEmbed = function(type, context, content){
 }
 
 // Adds formatted page numbers to the embed footer
+/**
+ * Formats embeds for pagination.
+ * @deprecated No longer necessary in DynamicCardStack.
+ * @param embeds Array of Messages
+ * @returns {Embed[]}
+ */
 module.exports.formatPaginationEmbeds = function(embeds){
   // No formatting if we only have one page
   if(embeds.length == 1) return embeds;