Moved all error strings to src/errors/messages and a few other things (#1695)

* Added missing error messages
As well as `Guild#setRolePosition` and `Guild#setChannelPosition`'s first arg validation
And fixed a typo in `Guild#setChannelPosition`
`roles` -> `channels`

* Reverted collection and Util constructors

* Removed leftover messages
Should have been in the second commit.

* It's a single invalid permission and removed unused flag error

* Fix INVALID_TOKEN -> TOKEN_INVALID as of #1703

src/structures/VoiceChannel.js

@@ -1,5 +1,6 @@
 const GuildChannel = require('./GuildChannel');
 const Collection = require('../util/Collection');
+const { Error } = require('../errors');
 
 /**
  * Represents a guild voice channel on Discord.
@@ -113,7 +114,7 @@ class VoiceChannel extends GuildChannel {
    *  .catch(console.error);
    */
   join() {
-    if (this.client.browser) return Promise.reject(new Error('Voice connections are not available in browsers.'));
+    if (this.client.browser) return Promise.reject(new Error('VOICE_NO_BROWSER'));
     return this.client.voice.joinChannel(this);
   }