[MINOR] improved signature of getExchangeSubFolder
[FIX] changed semantics of config.folders.getExchangeFolder
[FEATURE] new base class for handling interactive updates
[FEATUER] pubchem updater implemented
[FEATURE] better testing of xcms installation and updates
[FEATURE] updaters.check_emzed_updates + ns cleanup
[FIX] fixed error in test_pubchem_update.py
[FIX] added missing files