Improve voronoi parser to include all core states in output

[PhilippRue]

So far we only keep the highest lying core state in the voronoi output:
https://github.com/JuDFTteam/masci-tools/blob/a950f492ecebcc1b15100e5dc891f5a6fa6c1a5b/masci_tools/io/parsers/voroparser_functions.py#L100

According to @pteronura this could lead to problems for rare earths when semi core states need special treatment (if two semicore states are too close to each other and should be included in the energy contour instead).