Add an option to disable animation

[TexDash]

Thanks for this wonderful tool!

I found that the animation is a little distracting. It would be nice to have the option to disable the animation, which makes the interaction more responsive and instant.

[GitFiend]

Do you turn off animations for your operating system? I've been considering respecting the users operating system setting and disabling animations if they are off there. Or would you prefer having an option/both?

[TexDash]

I usually use XFCE or KDE, with animation disabled. I think it would be great, and also more robust, to have an explicit option in GitFiend, since I am afraid it's not easy to detect the animation option of the OS, especially for so many different Linux flavors.