Don't expand @-codes automatically for all node messages/telegrams saved

This recent enhancement (Commit b27bd426) introduced security and usability
concerns.

So I created (and am now using where requested) a wrapper for formatting
text.dat/ini strings which will automaticlaly detect @-code encoded strings
and expand/use them *only* (instead of printf %-specifiers).

This might impact issue #696 since although unintentionally, it actually was
possible to mix @-codes and %-specifier usage in certain (node status)
text.dat/ini strings, but that should not be possible now. It's either/or:
@-codes or %-specifiers, not both.