Increase MP Command delay to 4 turns, decrease MP turns to 200ms.

To hide network latency, MP turns send commands not for the next turn
but N turns after that (introduced in c684c211a2).
Further, MP turn length was increased to 500ms compared to 200ms SP
turns (introduced in 6a15b78c98).
Unfortunately, increasing MP turn length has negative consequences:
- makes pathfinding/unit motion much worse & unit behaviour worse in
general.
- makes the game more 'lag-spikey', since computations are done less
often, but thus then can take more time.

This diff essentially reverts 6a15b78c98, instead increasing
COMMAND_DELAY from 2 to 4 in MP. This:
- Reduces the 'inherent command lag' in MP from 1000ms to 800ms
- Increases the lag range at which MP will run smoothtly from 500ms to
600ms
- makes SP and MP turns behave identically again, removing the
hindrances described above.

As a side effect, single-player was not actually using COMMAND_DELAY,
this is now done (can be used to simulate MP command lag).

Refs #3752

Differential Revision: https://code.wildfiregames.com/D3275
This was SVN commit r25001.

source/rlinterface/RLInterface.cpp

@@ -389,7 +389,7 @@ void Interface::ApplyMessage(const GameMessage& msg)
 				turnMgr->PostCommand(command.playerID, commandJSON);
 			}
 
-			const u32 deltaRealTime = DEFAULT_TURN_LENGTH_SP;
+			const u32 deltaRealTime = DEFAULT_TURN_LENGTH;
 			if (nonVisual)
 			{
 				const double deltaSimTime = deltaRealTime * g_Game->GetSimRate();