Supertest: Soviet tech tree changes

A branch of researchable heavy tanks has been added. The new heavy tank branch will start with the Tier VII KV-3 tank and include the following vehicles:

Tier VIII: Object 703 II (premium);
Tier VIII: IS-2-II (standard);
Tier IX: IS-3-II (standard);
Tier X: ST-II (standard).

It is estimated that ~ 65,000 XP will be needed for researching the tier VIII.