qml: Update animation implementation

This MR adds speed and generic durations to our QML frontend.

This allows us to enable / disable animations and increase / decrease their speed from a single place. We are also adding generic properties with the most frequently used ones, like 150ms or 200ms.

As a best practice, contributors should ponder whether their animation fits into these before redeclaring a specifig timing. Maybe there is already a few that we could streamline to generic ones. But this MR does not change anything in that regard.