Add more libinput options, especially "scroll_button" and "scroll_factor"

[Schweber]

I'd like to have more options to change the behaviour of libinput, as this is a huge QoL improvement for me. For me, this is way more important than animations, looks etc. (i'm not using them anyway).

[YaLTeR]

You could try adding them yourself if you want; they should be pretty straightforward to add similarly to other libinput options, e.g. cc83ff0

[chillinbythetree]

Hey. I added the scroll_button property. I'm currently using it with my trackball and it works great. It will be available in the next release but you can use it now if you compile it from git.

#744

Someone is working on implementing scroll_factor. You can follow the progress here:

#730