Add kinetic scrolling to resource item choosers

Users can now enable a setting inside General > Tools that will allow them to use kinetic scrolling (using touch-and-drag or click-and-drag) inside resource item choosers like the brush presets panel; this can be less fiddly than using the scrollbar (e.g. when using a stylus).

Differential Revision: https://phabricator.kde.org/D8015