[Technical-Support] LPS-48330 "layoutIds" hidden field won't contain checked pages correctly when pages tree doesn't load all selected nodes at first time

Hi Dani,

Please review these commits.

There are a new public and a new protected methods in ExportImportHelperImpl.java.

-  createLayoutsJSON: This methods will be called when actual layout has children. Don't forget that a layout's  "includeChildren" property will only be true if it's all children are checked and all children's "includeChildren" property is true or actual layout has not any children.

- getSelectedLayoutsJSON: This create a String from the generated JSONArray.

Thanks,
 Zsaga