Backport AppTek changes to LM + LM lookahead code

[curufinwe]

Originally I wanted to only backport some fixes I made to the cheating LM, s.t. you can also do search-error experiments, but this escalated to many more changes in the LM codebase + some search related stuff. I tested that everything still compiles (in an appropriate singularity image), but it would be good if one / multiple of you could check if they get the same recognition results as before.