Suggestion to add warning when crystal symmetry information is missing while importing structures in xyz file format.

When exporting an xyz file from Aiidalab, no crystal symmetry information is stored. If this file is used to import a structure back into Aiidalab, the software automatically creates a periodic structure. However, it assumes a rectilinear symmetry, which is not always true. It would be helpful if a warning was issued when no crystal symmetry information is found and the aiidalab creates this info.