feat: tidy things up and implement more renderers

- Finished Library parser
- Fixed search continuations
- Improved channel parser
- Improved playlist parser
- Added support for posts of type poll
- Improved History parser
- Removed redundant code

lib/parser/contents/classes/GridChannel.js

@@ -1,4 +1,7 @@
+'use strict';
+
 const Author = require('./Author');
+const Parser = require('..');
 const NavigationEndpoint = require('./NavigationEndpoint');
 const Text = require('./Text');
 
@@ -12,8 +15,9 @@ class GridChannel {
       navigationEndpoint: data.navigationEndpoint
     }, data.ownerBadges, data.thumbnail);
     this.subscribers = new Text(data.subscriberCountText);
-    this.videos = new Text(data.videoCountText);
+    this.video_count = new Text(data.videoCountText);
     this.endpoint = new NavigationEndpoint(data.navigationEndpoint);
+    this.subscribe_button = Parser.parse(data.subscribeButton);
   }
 }