Support new LED sysfs node format

[jigpu]

As described in the README, the new sysfs nodes are already world-readable and so don't rely on the ekr_fixperm program.

[jtoman]

I recently updated the ekr_monitor script from this repo to support the new format, and added some extra features (you can configure stylus buttons now). Should I open a pull request or does it make sense to have a different repo?