[KPhotoAlbum] Tuning down scrolling speed in ThumbnailView.

[Andreas Neustifter]

Hi all!

When mouse-wheel-scrolling through my images I constantly loose track
because the scrolling is page-wise (per "wheel-click"). I propose a
patch that reduces scrolling speed such that one "wheel-click" does
only scale a fifth of the screen.

https://github.com/astifter/kphotoalbum-fork/commit/80c8e2139fc18820469678177bd176a88cec40d8

Andi

PS: I adapted the link-to-github version to present my patches, if
this is to confusing for everyone I will switch back to the
traditional patch-sending.