Beta 0.82: Mi-24, Ka-50 and Tutorial

Beta 0.82

New Units:

1. Mi-24: Gunship with high hp and low speed, equip 2 weapons at the same time, gatting cannon and air-to-surface rocket launcher.
2. Ka-50: Gunship with high hp and low speed, equip 2 weapons at the same time, gatting cannon and air-to-surface rocket launcher.

Features:

1. Tutorial Map: Introducing basic functions of the game, help new players.
2. Easy Mode: Add easy level to the AI, which will be very slow in building and training.

Balance:

1. BMP-1 cost increased from 600 to 700, adding a missile launcher as secondary weapon.
2. BTR-90 cost increased from 750 to 1000, adding a missile launcher as secondary weapon.
3. Javelin launcher cost increased from 350 to 600, damage increased from 350 to 600.

Bug Fix:

1. Fix OSA has wrong price when training in factory.
2. Fix vehicle and weapon trait text were not shown in Armory.