[NUI] Fix button bugs and improve switch.

[NUI] Fix button bugs and improve switch.

* Button's IconOrientation bug
In the previous code, when the IconOrientation property changed,
the LayoutItems() was called and it created a new layout.
But in case the button was inside another layout, the behaviour
described above caused unexpect look. Therefore I fixed it
by changing orientation related properties to the existing layout
instead of creating a new layout.

* Improve switch and extension relationship
The switch extension does not register any event handler to the switch components anymore.

Signed-off-by: Jiyun Yang <ji.yang@samsung.com>