title: No Drawable, NinePatch, TextureRegion, Texture, or Sprite registered with name: selection in json user skin?
body: <p>I'm trying to set the style of my UI with JSON.</p>
  
  <p>In this tutorial: <a href="http://www.gamefromscratch.com/post/2013/12/18/LibGDX-Tutorial-9-Scene2D-Part-3-UI-Skins.aspx" rel="nofollow">http://www.gamefromscratch.com/post/2013/12/18/LibGDX-Tutorial-9-Scene2D-Part-3-UI-Skins.aspx</a>
  The uiskin.json doesn't work for me. I removed all the other styles that i don't need and this is my actual skin code:</p>
  
  <p>uiskin.json:</p>
  
  <pre><code>{
      com.badlogic.gdx.graphics.g2d.BitmapFont: {
          default-font: {
              file: AlanDen50.fnt
          }
      },
      com.badlogic.gdx.graphics.Color: {
          green: {
              a: 1,
              b: 0,
              g: 1,
              r: 0
          },
          blue: {
              a: 1,
              b: 1,
              g: 0,
              r: 0
          },
          white: {
              a: 1,
              b: 1,
              g: 1,
              r: 1
          },
          red: {
              a: 1,
              b: 0,
              g: 0,
              r: 1
          },
          black: {
              a: 1,
              b: 0,
              g: 0,
              r: 0
          }
      },
      com.badlogic.gdx.scenes.scene2d.ui.TextButton$TextButtonStyle: {
          default: {
              font: default-font,
              fontColor: blue,
              downFontColor: red
          }
      },
      com.badlogic.gdx.scenes.scene2d.ui.Label$LabelStyle: {
          default: {
              font: default-font,
              fontColor: blue
          }
      },
      com.badlogic.gdx.scenes.scene2d.ui.TextField$TextFieldStyle: {
          default: {
              selection: selection,
              font: default-font,
              fontColor: blue,
              cursor: cursor
          }
      }
  }
  </code></pre>
  
  <p>and this is PlayScreen.java:</p>
  
  <pre><code>    Skin skin = new Skin(Gdx.files.internal("data/uiskin.json"));
  
      TextField inpName = new TextField("Nome", skin);
      inpName.setBounds(300, 200, 200, 40);
  </code></pre>
  
  <p>The errors I get is:</p>
  
  <pre><code>Exception in thread "LWJGL Application" com.badlogic.gdx.utils.SerializationException: Error reading file: data/uiskin.json
      at com.badlogic.gdx.scenes.scene2d.ui.Skin.load(Skin.java:96)
      at com.badlogic.gdx.scenes.scene2d.ui.Skin.&lt;init&gt;(Skin.java:73)
      at com.me.dunbar.MenuScreen.show(MenuScreen.java:43)
      at com.badlogic.gdx.Game.setScreen(Game.java:62)
      at com.me.dunbar.DunBarGame.switchScreen(DunBarGame.java:32)
      at com.me.dunbar.DunBarGame.create(DunBarGame.java:16)
      at com.badlogic.gdx.backends.lwjgl.LwjglApplication.mainLoop(LwjglApplication.java:136)
      at com.badlogic.gdx.backends.lwjgl.LwjglApplication$1.run(LwjglApplication.java:114)
  Caused by: com.badlogic.gdx.utils.SerializationException: Error reading file: data/uiskin.json
      at com.badlogic.gdx.utils.Json.fromJson(Json.java:658)
      at com.badlogic.gdx.scenes.scene2d.ui.Skin.load(Skin.java:94)
      ... 7 more
  Caused by: com.badlogic.gdx.utils.SerializationException: Serialization trace:
  selection (com.badlogic.gdx.scenes.scene2d.ui.TextField$TextFieldStyle)
      at com.badlogic.gdx.utils.Json.readFields(Json.java:758)
      at com.badlogic.gdx.utils.Json.readValue(Json.java:861)
      at com.badlogic.gdx.scenes.scene2d.ui.Skin$1.readValue(Skin.java:411)
      at com.badlogic.gdx.utils.Json.readValue(Json.java:805)
      at com.badlogic.gdx.scenes.scene2d.ui.Skin$2.readNamedObjects(Skin.java:432)
      at com.badlogic.gdx.scenes.scene2d.ui.Skin$2.read(Skin.java:421)
      at com.badlogic.gdx.scenes.scene2d.ui.Skin$2.read(Skin.java:417)
      at com.badlogic.gdx.utils.Json.readValue(Json.java:835)
      at com.badlogic.gdx.scenes.scene2d.ui.Skin$1.readValue(Skin.java:411)
      at com.badlogic.gdx.utils.Json.fromJson(Json.java:656)
      ... 8 more
  Caused by: com.badlogic.gdx.utils.GdxRuntimeException: No Drawable, NinePatch, TextureRegion, Texture, or Sprite registered with name: selection
      at com.badlogic.gdx.scenes.scene2d.ui.Skin.getDrawable(Skin.java:284)
      at com.badlogic.gdx.scenes.scene2d.ui.Skin.get(Skin.java:132)
      at com.badlogic.gdx.scenes.scene2d.ui.Skin$1.readValue(Skin.java:410)
      at com.badlogic.gdx.utils.Json.readFields(Json.java:751)
      ... 17 more
  </code></pre>
  
  <p>Now, if I delete 'selection' and 'cursor' from json the app runs but I don't see any text field!</p>
  
  <p>I'm using the gdx nightly build (22 dec 2013) but this wasn't working even in 0.9.9 stable.</p>