download: reworked connection:

- added shareable code with default proxy, headers and other settings for download tasks like images, symbols, mtgjson, etc;
- use XmageURLConnection.downloadText for text resources
- use XmageURLConnection.downloadBinary for any file resources
- added user agent with app version for all requests;
- added http logs and improved error messages;

Mage.Verify/src/main/java/mage/verify/mtgjson/MtgJsonMetadata.java

@@ -1,9 +1,15 @@
 package mage.verify.mtgjson;
 
+/**
+ * MTGJSON v5: metadata class
+ * <p>
+ * Contains version info
+ * <p>
+ * API docs <a href="https://mtgjson.com/file-models/meta/">here</a>
+ *
+ * @author JayDi85
+ */
 public final class MtgJsonMetadata {
-    // MTGJSON metadata
-    // https://mtgjson.com/file-models/meta/
-
     public String date;
     public String version;
 }