V2.1 update

- removed required "Row Class Attribute" form context XML
- hide control bar buttons of Microflows of type "selection" (single
select data grid)
- Shared array conflicting with multiple widgets in a page (toolbar
buttons)
- Enable data grid extension to work on reference set selector too.
- Can hide / show grid buttons when a grid is empty or not with the
classes "hideOnEmpty" or "showOnEmpty"
- When paging is hidden in modeller and dynamic hiding is enabled
resulted in an error
- empty table header can be hidden without showing a button.