Change virial output

[brucefan1983]

• Output virial data in 12 columns instead of 2: the first 6 columns for NEP prediction and the last 6 for reference. Ordered as xx, yy, zz, xy, yz, zx.
• Output dipole data in 6 columns instead of 2: the first 3 columns for NEP prediction and the last 3 for reference. Ordered as x, y, z.
• Output polarizability data in 12 columns instead of 2: the first 6 columns for NEP prediction and the last 6 for reference. Ordered as xx, yy, zz, xy, yz, zx.
• Allow for missing dipole and polarizability reference data for the prediction mode.

[shdchen]

Looks nice. Passed some quick tests on carbon and HCNOSCl.

[brucefan1983]

Looks nice. Passed some quick tests on carbon and HCNOSCl.

thanks for testing and fixing a typo.