elm_spinner: change the key event operation on spinner

elm_spinner: change the key event operation on spinner

Left/Right(or Up/Down with vertical one) changed the value of
spinner previously. However, it gave uneasy because focus could not be
moved to another winset until the value met the min or max.
Now, inc/dec button can get focus, and enter input on them change
the value.
Additionally, central text button changes to the entry automatically
when it gets focus. i.e. toggle on the text button is removed.

@fix