balance stick - infantry, mammoth

During playtesting it seemed like having infantry go at full speed on clear terrain was a good addition.
If it seems inappropriate for some infantry, can change it individually later for some units that might be too fast (e.g. flamethrowers and grenadiers, who travel at speed=5).

Mammoth tank turret rotation speed increased to 3, matching its rotation speed. Seems like a good idea so that mammoth is more reliable as GDI's heavy anti-air unit.