Quickopen delay

[Sven Brauch]

Hi there!

Since a while, we have this 150ms delay for quickopen: only if you
type nothing for 150ms or more, the list gets updated. The change was
introduced because for large projects, the UI gets sluggish when the
list is updated on every keypress.

I don't like this change. Especially the outline widget felt much more
responsive before, and there the change is totally unnecessary because
of the low item-count.

The reasons why I find it annoying in particular are:

 * If you type something that has no matches. Depending on how fast
you type, you may well type four or five more chars before the list
gets updated (remember, the timer is reset each time you press a
key!), just to see that you need to delete them again. (example: type
"foobar" into any document's outliner. I can type the whole word
before the list turns empty, telling me there's no matches)

 * If you want to continuously delete a part of the expression until
more matches appear. It is substantially harder to stop at the right
place with the delay. (example: type anything into any file's outliner
and try to quickly delete chars at the end until more items appear in
the quickopen list, while stopping as soon as that happens)

My proposed change is to make the delay depend on how many items need
to be searched: https://git.reviewboard.kde.org/r/104486/
Milian doesn't like it, arguing that the timeouts are just randomly
choosen and that a 150ms delay is unnoticeable anyways (that's why I
write this mail, to ask for more opinions).

Please, try the two versions (with the patch and without it)
side-by-side. It's very hard to imagine the difference if you've been
using either version for a while. Some user at IRC yesterday also
stated the delay is totally unnoticeable, until he tried the patched
version and agreed it feels noticeably smoother with it.

Greetings,
Sven