implemented EXT-4523 Log for all Ad-Hoc conferences is stored in one file

* for outgoing ad-hoc sessions chat history is saved into new file for every distinct set of initial participants
format: ["Ad-hoc Conference" "hash"<md5 hash of sorted participants' UUIDs>.txt]
ex: Ad-hoc Conference hash77a0ff26-614d-0dbd-ce19-5da9108f141a.txt

* for incoming ad-hoc sessions, chat history of each session is saved into a separate file:
format: [<ad-hoc session name> <timestamp> <4 first symbols of session id>.txt]
ex: Igor ProductEngine Conference 2010_01_22 07_41 2752.txt

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branch : product-engine