Overhaul channel typing system (#576)

* Overhaul channel typing system

* Fix ESLint error

* Add channel.isTyping()

* Add count argument to startTyping

* Add range checking to startTyping count

* Better range checking for count

* Add channel.getTypingCount()

* Change getTypingCount() to typingCount getter

* Switch isTyping() to typing getter

* Fix new methods and switch to Map

* Fix applyProp so getters/setters will work

* Add default value to force

src/structures/DMChannel.js

@@ -63,7 +63,19 @@ class DMChannel extends Channel {
     return;
   }
 
-  setTyping() {
+  startTyping() {
+    return;
+  }
+
+  stopTyping() {
+    return;
+  }
+
+  get typing() {
+    return;
+  }
+
+  get typingCount() {
     return;
   }