Add support for writing bond information in Lammps data files

This PR adds support for writing bond information in Lammps data files with style = 'full'.

The code assumes that the bond information is kept in arrays['bonds'] in the same format in which it is read by read_lammps_data. As a matter of fact, the following code preserves the bond information:

import ase.io
atoms=ase.io.read("ase/test/testdata/lammpsdata_input.data",format='lammps-data',atom_style="full")
ase.io.write("out.lammps-data",atoms,atom_style='full')

I added a new boolean optional argument 'bonds' to the method write_lammps_data, to choose whether to write bond information or not. The default is currently set to True. This is because lammps and ovito follow the same convention: if bond information is present and atom_style = 'full' then bond information is relevant and thus is written. The default can be changed to False to improve backward compatibility at the expense of less intuitive behavior.

Checklist

• I am familiar with ASE's contribution guidelines.
• Doc strings in code changed in this MR are up to date.
• Unit tests have been added for new or changed code.