Simplify obs-classic configuration page (in preparation for variants)

[opatut]

I rewrote the configuration pages, joining the subpages into one.

This is in preparation of explaining configuration for all OBS variants, so it is easier to navigate. Also, this removes quite a bit of duplication, and IMO is just easier to understand.

I've removed the screenshots as I feel they added very little value and a lot of distraction.