Implement logic to display path(s) connecting two components belonging to a (PyPSA) network

[ricnogfer]

PyPSATopo should provide the capability to display the path(s) connecting two components (specified by the user) when generating the topographical representation of a network (and exclude all other paths that do not connect the components from this representation). By default, PyPSATopo should display all paths but additional functionalities should be provided, namely:

1. Only display the shortest path between two components.
2. Only display the longest path between two components.