Implement ChanneldWorldSettings

[indiest]

What

A place to store the settings of the view class, server groups, and channeld launch args individually for each map.

Why

In a project with multiple maps that have different channel settings (e.g. the demos project), opening and testing different maps in the editor can be troublesome - if a developer forgets to set the view class, the server groups, or the channeld launch args properly every time opening a map, s/he may fail to run the map.

How

Save the settings per map. WorldSettings is instantiated per map, and can be extended easily.

Things to discover:

• Is it able to get the WorldSettings instance from the editor code?
• Add #if WITH_EDITORONLY_DATA for the server groups and channeld launch args and see if they are saved and loaded properly