Beta 0.91 G-6 mobile artiilery

Beta 0.91

New Unit: G-6: Howitzer that with fast speed and short prepare fire time.

New Feature: Enhanced AI, more intelligent.

Bug Fix: For Mac version, menu and dock do not spread out the mouse the on the top or buttom. Easy AI now can attack player's base now. Fixed some spelling error.

Balance: Increase the cost of all artillery units. Scud-B cost increased from 5000 to 6000. M1A2 tank now have the trait of +100% repair effect. Hummv now have the trait of +100% repair effect.