Refactor extractor

- Refactor info classes and extractors
- Reformat and fix indentation
- Organize packages and classes
- Rename variables/methods and fix regex
- Change the capitalization
- Add methods to playlist extractor

playlist/PlaylistInfoItemExtractor.java

@@ -0,0 +1,9 @@
+package org.schabi.newpipe.extractor.playlist;
+
+import org.schabi.newpipe.extractor.exceptions.ParsingException;
+
+public interface PlaylistInfoItemExtractor {
+    String getThumbnailUrl() throws ParsingException;
+    String getPlaylistName() throws ParsingException;
+    String getWebPageUrl() throws ParsingException;
+}