Reduce the timeout in KItemListKeyboardSearchManager to 1 second

Reduce the timeout in KItemListKeyboardSearchManager to 1 second

It turned out that the longer timeout, introduced recently in
02eab49b2de51c31fe46a0d9501327b579b3648e, not only made multi-letter
keyboard searches easier, but also had some unwanted side effects. I
hope that 1 second, which is between the previous value of 5 seconds and
the pre-KDE 4.8.2 value of 0.4 seconds, is a compromise which will fit
most users' needs.
We will try to improve the situation further in future releases by
providing visual feedback about the keyboard search, but such a change
would not be suitable for a bug-fix release.
(cherry picked from commit d8732a59d3b1f2d0bebf43f294df7e9f333abde4)