Add showSoftKeyboard(boolean show) to JmeSystem.

Includes empty implementations for now.  Android to be implemented in next commit.

jme3-android/src/main/java/com/jme3/system/android/JmeAndroidSystem.java

@@ -230,4 +230,8 @@ public class JmeAndroidSystem extends JmeSystemDelegate {
     public static String getAudioRendererType() {
         return audioRendererType;
     }
+
+    @Override
+    public void showSoftKeyboard(boolean show) {
+    }
 }

jme3-core/src/main/java/com/jme3/system/JmeSystem.java

@@ -103,6 +103,11 @@ public class JmeSystem {
         systemDelegate.setSoftTextDialogInput(input);
     }
 
+    public static void showSoftKeyboard(boolean show) {
+        checkDelegate();
+        systemDelegate.showSoftKeyboard(show);
+    }
+
     public static SoftTextDialogInput getSoftTextDialogInput() {
         checkDelegate();
         return systemDelegate.getSoftTextDialogInput();

jme3-core/src/main/java/com/jme3/system/JmeSystemDelegate.java

@@ -179,4 +179,6 @@ public abstract class JmeSystemDelegate {
     public abstract void initialize(AppSettings settings);
 
     public abstract ImageRaster createImageRaster(Image image, int slice);
+
+    public abstract void showSoftKeyboard(boolean show);
 }

jme3-desktop/src/main/java/com/jme3/system/JmeDesktopSystem.java

@@ -328,4 +328,8 @@ public class JmeDesktopSystem extends JmeSystemDelegate {
         }
         logger.log(Level.INFO, "Running on {0}", getFullName());
     }
+
+    @Override
+    public void showSoftKeyboard(boolean show) {
+    }
 }

jme3-ios/src/main/java/com/jme3/system/ios/JmeIosSystem.java

@@ -110,4 +110,9 @@ public class JmeIosSystem extends JmeSystemDelegate {
     public ImageRaster createImageRaster(Image image, int slice) {
         throw new UnsupportedOperationException("Not supported yet.");
     }
+
+    @Override
+    public void showSoftKeyboard(boolean show) {
+        throw new UnsupportedOperationException("Not supported yet.");
+    }
 }