replaced hard coded style with a css rule

svn changeset:15308/svn branch:6.4

WebContent/VAADIN/themes/base/button/button.css

 /*
  * Checkbox styles
  * -------------------------------------- */
+ 
+ .v-checkbox {
+ 	display: block;
+ }
 
 .v-checkbox,
 .v-checkbox label,

src/com/vaadin/terminal/gwt/client/ui/VCheckBox.java

 
     private Icon icon;
 
-    private boolean isBlockMode = false;
-
     private HandlerRegistration focusHandlerRegistration;
     private HandlerRegistration blurHandlerRegistration;
 
 
     @Override
     public void setWidth(String width) {
-        setBlockMode();
         super.setWidth(width);
     }
 
     @Override
     public void setHeight(String height) {
-        setBlockMode();
         super.setHeight(height);
     }
 
-    /**
-     * makes container element (span) to be block element to enable sizing.
-     */
-    private void setBlockMode() {
-        if (!isBlockMode) {
-            DOM.setStyleAttribute(getElement(), "display", "block");
-            isBlockMode = true;
-        }
-    }
-
     public void onFocus(FocusEvent arg0) {
         client.updateVariable(id, EventId.FOCUS, "", true);
     }