Integrate BFS algorithm into board builder

[Rampex1]

Currently, board builder cannot find the position of markers with no direct relation to the reference marker (haven't appeared in the same frame). This can be solved with a BFS search algorithm which I have in board_builder/utils/graph_search.py. A test case has been written in board_builder/test/graph_search_test.py to demonstrate the feasability of the algorithm. All that's left is to implement it in board builder, in the method build_board().