add option to use fake locking (utils.NoCM)
add more models; enable passing model parameters
allow retrieving vector by id in SessionServer
allow similarity queries by topic distribution
delete payload file as well on drop_index
add get_tfidf method
* return only weighted BOW, even if the final model continues with further transformations (LDA/LSI)
better handling on max_results/num_best/topsims settings
* but still too complex, will rework and simplify the logic later