[IETANKS-35] add initial board-related interfaces

Board, Tank and Projectile interfaces are the ones used by rest of game system
 * Board has getBoard method returning "some" representation of Board
 * Projectile has shotBy method which returns id of tank, which shot the bullet
Merge pull request #1 from artekorzel/board

Board model
Merge pull request #3 from Mequrel/technical/gameplay-related-modules

Gameplay related modules
First draft of the engine interface
Interface moved to api directory
Created the interface for engine module. Implemented extremely simple game logic (only move to right)