Further Pushing tweaks: more customisable, longer ranges.

This overall decreases the deathball effect from units walking to each other a bit.

• Fix formations - this cleans up a UnitMotion hack for formations, making it possible to increase pushing ranges without breaking closely knit formations like testudo.
• Make MINIMAL_PUSHING and the MOVE_EXTENSION configurable, and add a STATIC_EXTENSION as well.
• Increase the pushing range significantly, making units sparser.

Differential Revision: https://code.wildfiregames.com/D4098