Update @since tags to 7.5.6.

Change-Id: I376cd27d5ae08c877cd3279740b601fb8dddb2e7

client/src/com/vaadin/client/ComputedStyle.java

     /**
      * Returns the sum of the top and bottom margin
      * 
-     * @since 7.6
+     * @since 7.5.6
      * @return the sum of the top and bottom margin
      */
     public double getMarginHeight() {
     /**
      * Returns the sum of the top and bottom margin
      * 
-     * @since 7.6
+     * @since 7.5.6
      * @return the sum of the left and right margin
      */
     public double getMarginWidth() {

client/src/com/vaadin/client/LayoutManager.java

     /**
      * Checks if there is something waiting for a layout to take place.
      * 
-     * @since
+     * @since 7.5.6
      * @return true if there are connectors waiting for measurement or layout,
      *         false otherwise
      */

client/src/com/vaadin/client/ui/VFilterSelect.java

          * by a server-side {@link com.vaadin.ui.ComboBox.ItemStyleGenerator}.
          * The returned style is prefixed by <code>v-filterselect-item-</code>.
          * 
-         * @since
+         * @since 7.5.6
          * @return the style name to use, or <code>null</code> to not apply any
          *         custom style.
          */

server/src/com/vaadin/ui/AbstractSelect.java

          * Item caption mode: Item's ID's <code>String</code> representation is
          * used as caption.
          * 
-         * @since
+         * @since 7.5.6
          */
         ID_TOSTRING,
         /**

server/src/com/vaadin/ui/ComboBox.java

      * shown in the popup. The CSS class name that will be added to the item
      * style names is <tt>v-filterselect-item-[style name]</tt>.
      * 
-     * @since
+     * @since 7.5.6
      * @see ComboBox#setItemStyleGenerator(ItemStyleGenerator)
      */
     public interface ItemStyleGenerator extends Serializable {
      * @param itemStyleGenerator
      *            the item style generator to set, or <code>null</code> to not
      *            use any custom item styles
-     * @since
+     * @since 7.5.6
      */
     public void setItemStyleGenerator(ItemStyleGenerator itemStyleGenerator) {
         this.itemStyleGenerator = itemStyleGenerator;
      * 
      * @return the itemStyleGenerator the currently used item style generator,
      *         or <code>null</code> if no generator is used
-     * @since
+     * @since 7.5.6
      */
     public ItemStyleGenerator getItemStyleGenerator() {
         return itemStyleGenerator;

uitest/src/com/vaadin/tests/customelements/CustomProgressBarElement.java

     }
 
     /**
-     * @since
+     * @since 7.5.6
      * @param indicator
      * @param string
      * @return