Added a dropdown menu class, similar to the one in osu!.

Using 'fa-chevron-down' and 'fa-chevron-right' icons from Font Awesome v4.4.0 (https://github.com/FortAwesome/Font-Awesome).

The dropdown menu is currently used only in the downloads menu to select servers.

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

src/itdelatrisu/opsu/downloads/servers/DownloadServer.java

@@ -75,4 +75,7 @@ public abstract class DownloadServer {
 	public String getPreviewURL(int beatmapSetID) {
 		return String.format(PREVIEW_URL, beatmapSetID);
 	}
+
+	@Override
+	public String toString() { return getName(); }
 }