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 rP).
Further, MP turn length was increased to 500ms compared to 200ms SP turns (introduced in rP7551).
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 rP8400, 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