[New Feature] Add `SideBarSide` to allow map-makers to override the players sidebar theme.

[CCHyper]

Description:

Tiberian Sun already has a map INI key called SpeechSide which allows the map-maker to override the player houses speech set. A new INI key to also allow the sidebar artwork to be overridden would be a good addition to this and add more control to map-makers.

Possible Implementation:

Adding the INI key SpeechSide to ScenarioClass, which would be loaded from the scenario INI.