Fixed DataStore, deprecation leftovers and a bit of Event Constants (#1841)

* Fixed leftover fetchThing and removed unused methods/error messages

* Added resume event constant and used event constants wherever possible

* Replaced mentions of removed method name with their new name.

* Fixed typo: resume -> resumed

src/util/Constants.js

@@ -196,6 +196,7 @@ exports.VoiceOPCodes = {
 
 exports.Events = {
   READY: 'ready',
+  RESUMED: 'resumed',
   GUILD_CREATE: 'guildCreate',
   GUILD_DELETE: 'guildDelete',
   GUILD_UPDATE: 'guildUpdate',