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/ItemSection.js

@@ -7,8 +7,10 @@ class ItemSection {
   
   constructor(data) {
     this.header = Parser.parse(data.header);
-    this.target_id = data.targetId || data.sectionIdentifier || null;
     this.contents = Parser.parse(data.contents);
+    
+    data.targetId || data.sectionIdentifier && 
+      (this.target_id = data.targetId ? data.sectionIdentifier : null);
   }
 }