Modernize splash screen or remove it altogether

Current KMyMoney splash screen is very dated: https://techbase.kde.org/images.techbase/a/a4/Kmm_5_splash.png

Some effort was made in the past to modernize it (https://phabricator.kde.org/T4302, https://forum.kde.org/viewtopic.php?f=285&t=119635&start=120) but the discussion was abandoned due to the art rework that KDE was undergoing at a time.