21.6, PowhegControl: two fixes (lhe comments and gridpack handling)

This MR hopefully fixes two issues:

• The feature which fixes the comment lines in the produced files (some were buggy after reweighting, which makes Pythia crash) wasn't always working properly. Especially it seems there is now a new one #matching to handle. It is still possible to remove these lines completely (and info message is added to inform the user).
• The feature which informs if a gridpack is used or not (needed for the MCJoboption workflow) wasn't working properly. It relies on a list of .dat file name patterns which seemed incompatible with multi-core production of gridpack. It should hopefully also fix the issue of having meaningless symlinks contained in the produced gridpack (which was due to having the same file name patterns twice in the gridpack creator).