BFM file input hardening

[mxmlnkn]

There are multiple smaller problems which result in a simple segfault instead of any graceful shutdown. This list will be extended the more I find:

• I think I saw a segfault when changing e.g. 19 27 36 R under !mcs to 19 27 36 i.e. if the space separator is missing, even though it is not needed
• Number 13 can't be used as a bondID in a bond set, because it is the newline character. I guess it's to be expected, but not user-friendly when creating BFM-files