Add n.shapes

[drifter089]

Add new n.shapes PyPSA feature in PyPSA-Eur

Checklist

• [ ] following @FabianHofmann advice starting with build_bus_regions.py and cluster_network.py.
• [ ] duplicate data of all .geojson files in network.shape while checking file size.
• [ ] incrementally shift operation that are being done on geojson file to n.shapes Geopandas Dataframe directly.
• [ ] remove need for geojson files completely.
• [ ] improve plotting by using these new Geopandas related functions and libraries.
• [ ] A release note doc/release_notes.rst .