feat(Emoji): add deletable getter

Backport for commit: fca6d3be56
From PR: #2535

src/structures/Emoji.js

@@ -1,5 +1,6 @@
 const Constants = require('../util/Constants');
 const Collection = require('../util/Collection');
+const Permissions = require('../util/Permissions');
 const Snowflake = require('../util/Snowflake');
 
 /**
@@ -76,6 +77,15 @@ class Emoji {
     return new Date(this.createdTimestamp);
   }
 
+  /**
+   * Whether the moej is deletable by the client user
+   * @type {boolean}
+   * @readonly
+   */
+  get deletable() {
+    return !this.managed && this.guild.me.hasPermission(Permissions.FLAGS.MANAGE_EMOJIS);
+  }
+
   /**
    * A collection of roles this emoji is active for (empty if all), mapped by role ID
    * @type {Collection<Snowflake, Role>}