====== Handler.calC(source,target) ======
  - Return the shortest path from source company to target company based on a weighted people social network.
  - Parameters
  -   - source: company id
  -   -   - Starting node
  -   - target: company id
  -   -   - Ending node
  - Return: path: list
  -   - List of shortest path.
  - Raises: NoPath: if no path exists between source company to target company.
  - Notes:
  -   - When calculate the shortest path between two companies, we use the chairmen or senior manager to represent the company in social network.