Add M600 settings and smooth_scroll and side_scroll to FeatureSettings

I tried to hack together the settings for M600 mouse, mostly ignorant about the correct way to do it - so, maybe there are things wrong with this, I don't know about it but I am eager to learn about it.
It seems as if ```check_feature_settings``` is supposed to extract the features automagically, making this redundant, but if so, then there is something different wrong on that end?

side-scroll is _not_ enabled in the description, as it would cause an ```invalid function``` error and cause the gui to disable all settings, and I did not find the cause yet.

I thought this is a starting point and someone else might have an idea how to progress from here or at least someone would tell me where I went wrong.