Fixes #1158.

Overloaded the BFSShortestPath#getPaths function to accept target vertex. Added logic to terminate the loop if target vertex is found. No extra test cases added as BFSShortestPath#getPath test case was already present in BFSShortestPathTest.java. I could see improvement of 43 times in the benchmarking tests for BFSShortestPath#getPath.

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