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

Extractor.java

@@ -0,0 +1,35 @@
+package org.schabi.newpipe.extractor;
+
+import org.schabi.newpipe.extractor.stream.StreamInfoItemCollector;
+
+import java.io.Serializable;
+
+public abstract class Extractor implements Serializable {
+    private final int serviceId;
+    private final String url;
+    private final UrlIdHandler urlIdHandler;
+    private final StreamInfoItemCollector previewInfoCollector;
+
+    public Extractor(UrlIdHandler urlIdHandler, int serviceId, String url) {
+        this.urlIdHandler = urlIdHandler;
+        this.serviceId = serviceId;
+        this.url = url;
+        this.previewInfoCollector = new StreamInfoItemCollector(urlIdHandler, serviceId);
+    }
+
+    public String getUrl() {
+        return url;
+    }
+
+    public UrlIdHandler getUrlIdHandler() {
+        return urlIdHandler;
+    }
+
+    public int getServiceId() {
+        return serviceId;
+    }
+
+    protected StreamInfoItemCollector getStreamPreviewInfoCollector() {
+        return previewInfoCollector;
+    }
+}