[M3C] Implement Desert Warfare

[balazskristof]

Implements Desert Warfare

It's messy.

[Susucre]

I would really appreciate some unit testing when adding such complex custom trigger. Doesn't need to be exhaustif but some ideas of tests:

• Sacrifice a Desert
• Sacrifice a non-Desert
• Have a Desert be destroyed from the battlefield
• Discard a Desert
• Discard a non-Desert
• Mill some cards, including a few Deserts and at least one non-Desert

[balazskristof]

Tests added, checks:

• token generation
• sacrifice (both in own and opponents' turn)
• destroy
• discard (both turns)
• cycling (both turns)
• mill (both turns)
• "lands are Deserts" effects (in this case with Dune Chanter)