More modular pathfinding

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The path finding is tightly coupled to game objects like Board, Terrain and Unit. This can be resolved by:

• [ ] Add an interface with which pathfinding algorithms can query the board. As a result, pathfinding algorithms no longer depend on the game object Board.
• [ ] The pathfinding algorithm should be provided with a game object (pointer) for which the path is computed. This can be passed on to the interface (see above) to control queries, e.g. if a unit can access a certain terrain type. (Only add this if necessary at the moment)

Technical thoughts:

• Interface could be named IBoardQueryable
• Use a game component (BoardQueryableComponent) added to the Board game object to encapsulate query-logic

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Changes so far:

• AbstractPathfinder has template parameter TSpatialRepresentation (e.g. Coordinates)
• AbstractPathfinder accepts an IWorldAdapter<TSpatialRepresentation> as query abstraction to the world (e.g. a Board)
• AStar and Node are adjusted to new interfaces

Not finished yet:

• Path is still bound to Coordinates but also requires template parameter TSpatialRepresentation
• IWorldAdapter is not finished yet and is adjusted when path finding is extended later on