Make a bare slider look the same as a scrollbar slider.

git-svn-id: http://urho3d.googlecode.com/svn/trunk@2671 3bd170d8-ddcf-f82c-f583-7a401ccf5608
Simplified the scrollbar slider definition.

git-svn-id: http://urho3d.googlecode.com/svn/trunk@2672 3bd170d8-ddcf-f82c-f583-7a401ccf5608