qml: uniformize animation durations

Simplifies duration definitions, we don't need 14 different durations, especially close values like 125 and 128 ms.

The remaining chosen values are aligned on Kirigami definitions

This also remove the ability to change/disable animation speed as this was here only for testing purpose, and create unnecessary property bindings on every duration.

Maybe some animations duration choice made in this MR would have been better suited a different duration (duration_fast -> duration_long or duration_short), I haven't put much thoughts into that and am open to suggestions.