Added an automatic updater for new releases.

opsu! will now check for updates upon launching, and will prompt the user to download and run a newer version, if available.
- The remote version file is just the filled "version" file, currently located in the gh-pages branch.
- The new version is downloaded to the working directory, and launched with ProcessBuilder.

Related changes:
- Added "file" property (containing the download URL) to "version" file.
- Added maven-artifact dependency for version comparisons.
- Added methods in Downloads class to retrieve the constructor parameters.
- Moved method for showing exit confirmation dialogs into UI.
- Moved method for reading from URLs into Utils.

Signed-off-by: Jeffrey Han <itdelatrisu@gmail.com>

src/itdelatrisu/opsu/downloads/Download.java

@@ -138,9 +138,19 @@ public class Download {
 			return;
 		}
 		this.localPath = localPath;
-		this.rename = rename;
+		this.rename = Utils.cleanFileName(rename, '-');
 	}
 
+	/**
+	 * Returns the remote download URL.
+	 */
+	public URL getRemoteURL() { return url; }
+
+	/**
+	 * Returns the local path to save the download (after renamed).
+	 */
+	public String getLocalPath() { return (rename != null) ? rename : localPath; }
+
 	/**
 	 * Sets the download listener.
 	 * @param listener the listener to set
@@ -187,9 +197,8 @@ public class Download {
 						rbc.close();
 						fos.close();
 						if (rename != null) {
-							String cleanedName = Utils.cleanFileName(rename, '-');
 							Path source = new File(localPath).toPath();
-							Files.move(source, source.resolveSibling(cleanedName), StandardCopyOption.REPLACE_EXISTING);
+							Files.move(source, source.resolveSibling(rename), StandardCopyOption.REPLACE_EXISTING);
 						}
 						if (listener != null)
 							listener.completed();