Refactor player tanks method
- Implemented Wot::Player::Tank class, that contains some data
  about player's tank.
- Used Wot::Player::Tank class to represent player's tanks, instead
  of Vehicle, that should contain complete data about a tank, and,
  furthermore, should be renamed to Tank.
- Renamed and changed Wot::Api.player_vehicles method.
- Removed useless methods from Parser class.
Refactor player achievements functionality
- Implemented Wot::Player::Achievement class.
- Used Wot::Player::Achievement class instead of Wot::Achievement.
- Removed useless files and methods.