Close animation duration config option

[NamorNiradnug]

Opening and closing animations currently use the same duration option.

[ammen99]

I am planning a redesign of how the animation options are handled (including making it easier to set per-view animation duration & animation type) so I am not sure I want to do a breaking change right now. I will leave the PR open until I finalize my thoughts on this matter, but I do not plan to merge before 0.9.

[ammen99]

Hello again and thanks for your PR! I have an alternative approach based on view properties (#2835) where you can use a simple IPC script to set the open/close/minimize duration and animation types for each view individually.

If you don't like IPC, I suppose we could also add window-rules for setting view properties (PRs welcome :)). In any case, I think properties are the way forward, as we already have way too many config options for the animations.