add webhooks v8 (#759)

* add webhook structure and getChannelWebhooks as well as getServerWebhooks

* add sendMessage

* add the ability to edit create and delete hooks

* remove server wide cache and add getter.

src/Structures/Webhook.js

@@ -0,0 +1,39 @@
+"use strict";
+
+import {Endpoints} from "../Constants";
+/* example data
+{
+  id: '164585980739846145'
+  name: 'wlfSS',
+  roles: [ '135829612780322816' ],
+  require_colons: false,
+  managed: true,
+}
+*/
+
+export default class Webhook {
+  constructor(data, server, channel, user) {
+    this.server = server;
+    this.channel = channel;
+    this.id = data.id;
+    this.user = user || data.user;
+    this.name = data.name;
+    this.avatar = data.avatar;
+    this.token = data.token
+  }
+
+  get getURL() {
+    return `https://canary.discordapp.com/api/webhooks/${this.channel.id}/${this.token.id}`;
+  }
+
+  toObject() {
+    let keys = ['id', 'name', 'avatar', 'token'],
+      obj = {};
+
+    for (let k of keys) {
+      obj[k] = this[k];
+    }
+
+    return obj;
+  }
+}