[ENHANCEMENT] Add .gro file support to the Gromacs converter

[MBartkowiakSTFC]

Is your feature request related to a problem? Please describe.
Currently, the Gromacs converter requires a PDB file as one of the inputs.

Describe the solution you'd like
A .gro file contains all the information needed by the converter, so it could be used instead of a .pdb file.

Describe alternatives you've considered
The support for the PDB files has to be improved anyway.

Additional context
However we proceed, one of the goals is to give the Gromacs converter the same atom type verification field that is already present in most other converters.