Do not hardcode the value on main function

src/com/sheepit/client/standalone/Worker.java

@@ -82,7 +82,7 @@ public class Worker {
 	private String extras = null;
 	
 	@Option(name = "-ui", usage = "Specify the user interface to use, default 'swing', available 'oneline', 'text', 'swing' (graphical)", required = false)
-	private String ui_type = "swing";
+	private String ui_type = GuiSwing.type;
 	
 	@Option(name = "-config", usage = "Specify the configuration file", required = false)
 	private String config_file = null;
@@ -261,7 +261,6 @@ public class Worker {
 		
 		config.setComputeMethod(compute_method);
 		
-		
 		if (config_file != null) {
 			if (new File(config_file).exists() == false) {
 				System.err.println("Configuration file not found.");
@@ -275,14 +274,14 @@ public class Worker {
 		
 		Gui gui;
 		switch (ui_type) {
-			case "oneline":
+			case GuiTextOneLine.type:
 				if (config.getPrintLog()) {
 					System.out.println("OneLine UI can not be used if verbose mode is enabled");
 					System.exit(2);
 				}
 				gui = new GuiTextOneLine();
 				break;
-			case "swing":
+			case GuiSwing.type:
 				if (java.awt.GraphicsEnvironment.isHeadless()) {
 					System.out.println("Graphical ui can not be launch.");
 					System.out.println("You should set a DISPLAY or use a text ui (via -ui oneline or -ui text).");