elm_interface_scrollable: add support for *jumping* into a scroller

elm_interface_scrollable: add support for *jumping* into a scroller

Until recently we have been only registering the border elements of the
graph, (so only the elements that don't have a neighboor). However this
lead to the situation that a scroller that is scrolled into the middle
(so not the x nor the y axis is scrolled to the max), is not accessable.

Now, we register all elements that have a neighboor in the outside.
The patch in the test suite is required in order to provide the correct
geometry to the implementation of efl_ui_focus_manager_sub.

Differential Revision: https://phab.enlightenment.org/D7360