Enables Onager and Mongonel to chop trees along side the Siege Onager. So no more relying on noobs in michi games.

Specifically for DM Michi games as its very fun and more competitive playing across the map instead of just in one hole.

Onager and Mongonel have attack value set to enable attacking trees just like the siege onager along with the ability to target trees. Also attack values for the Tree type have been added. None of this affects damage caused by the Onager and Mongonel to other players units/buildings.

Doesn't affect any additional elements to the game.