efl_ui_spotlight: add scroll_block to Manager_Scroll

To support blocking of scrolling movement, @property scroll_block has
been added to Manager_Scroll.
If scroll_block is set to be true, then scrolling movement by mouse
input is blocked.

Reviewed-by: Marcel Hollerbach <mail@marcel-hollerbach.de>
Differential Revision: https://phab.enlightenment.org/D9444