Permissions Cleanup (#1643)

* fix Permissions.add/remove, by completely changing what they do

* permissions cleanup

Removes overwrite._denied and overwrite._allowed in favor of overwrite.denied.bitfield and overwrite.allowed.bitfield

uses the modified Permissions.add and Permissions.remove to clean up existing code

fixes GuildMember.missingPermissions

changes Permissions add/remove to reverse loops for speed, changes resolve to allow the number 0 as a valid permission.

* Revert createChannel overwrite.allow / overwrite.deny for arrays of {allow:bitfield, deny:bitfield}

Documentation should be improved here, although I would need advice. I believe a overwrite object typedef is needed, to show the structure of the object, and also include that collections may be used for this, rather than arrays.

* api router fix for overwritePermissions

* add Permissions.freeze, and change all returned Permissions to immutable instances

* Make Permissions a permission resolveable

change role.permissions to be an instance of Permissions

* Make permissions.add/remove return a new instance if the instance is frozen

* Fix invalid error

* Update GuildChannel.js

* Update Guild.js

* fix bad merge

src/structures/PermissionOverwrites.js

@@ -29,20 +29,17 @@ class PermissionOverwrites {
      */
     this.type = data.type;
 
-    this._denied = data.deny;
-    this._allowed = data.allow;
-
     /**
      * The permissions that are denied for the user or role.
      * @type {Permissions}
      */
-    this.denied = new Permissions(this._denied);
+    this.denied = new Permissions(data.deny).freeze();
 
     /**
      * The permissions that are allowed for the user or role.
      * @type {Permissions}
      */
-    this.allowed = new Permissions(this._allowed);
+    this.allowed = new Permissions(data.allow).freeze();
   }
 
   /**