Set keyHandled on the terminal GUI

This allows us to block JEI processing key events such as "o", meaning
the GUI is not constantly toggled when interacting with a turtle.

Also clean up the widget code, as there's a lot of functionality here
which only is needed in CCEdu.

src/main/java/dan200/computercraft/client/gui/GuiTurtle.java

@@ -95,7 +95,7 @@ public class GuiTurtle extends GuiContainer
         }
         else
         {
-            m_terminalGui.keyTyped( c, k );
+            if( m_terminalGui.keyTyped( c, k ) ) keyHandled = true;
         }
     }
     
@@ -119,7 +119,7 @@ public class GuiTurtle extends GuiContainer
     public void handleKeyboardInput() throws IOException
     {
         super.handleKeyboardInput();
-        m_terminalGui.handleKeyboardInput();
+        if( m_terminalGui.handleKeyboardInput() ) keyHandled = true;
     }
 
     protected void drawSelectionSlot( boolean advanced )