Improve and enhance file-plotting API

[raphaelquast]

• unify syntax for
  • m.new_layer_from_file.GeoTIFF
  • m.new_layer_from_file.NetCDF
  • m.new_layer_from_file.CSV
  • ... and similarly for Maps.from_file....
• [maybe] detect file-type by file-ending and avoid explicit functions for each filetype?
  • is this feasible/useful or does it cause problems/confusion ?
• add more filetypes (from_hdf, from_zarr, etc.?)