KexiRecordNavigator handles mouse wheel event in horizontal direction by
moving to the next or previous record. However, it triggered the change
for every and all wheel events, even when the delta was tiny, and it
resulted in unwanted record changes.
This was particularly noticeable when using a trackpad in the report
view, that uses KexiRecordNavigator for pagination: even when trying to
keep the hand movement as vertical as possible to scroll the page, there
were a lot of times that the viewer moved to the next or previous page.
This commit, based on Qt’s QAbstractSlider, has a lower threshold for
the wheel’s delta and keeps an accumulator to smooth out consecutive