Make player settings clearer for Atlas RMS

[Philip]

Currently the "Random map" part of the Map section in Atlas doesn't indicate how to control the number of players (and their civs etc) that will be used when generating the map, and it's unintuitive that you have to switch to the Player section and edit the current map's settings to control it.

Maybe it would be sufficient for the "Random map" area to have a "Edit players" button that simply switches to the Player section (like the toolbar button) so people might be able to figure out they're linked, or some descriptive text, or something like that.

[ben]

(In [9649]) Adds player settings shortcut to Atlas map panel. Fixes #874 Tweaks some control positions and layouts for consistency