Das Meta information Feature

[MartinWenge]

Add a Feature with commonly used metainformation keys for bfm Files.

[tonimueller]

Maybe we could write a monomer extension which provides a type specification of the monomer, e.g linear chain, cross linker, solvent, dendrimer, A-type, B-type.
In the bfm file, one could then see which ID has which type and the corresponding feature explains with the metadata output that 0 corresponds to "linear chain".
Moreover this could be helpful for a "grouping by tag" where a functor could be implemented which sorts by the monomer type.
In this manner, it is easy to get all cross-link IDs for further analyzes or all linear chains, also after the connection process (otherwise one could just use the sorting by connection in the unconnected state).