Cleaning up stale sessions more rarely.
Added API for generating a new session ID. (#212)
Generating session IDs on user track and removing them when user is lost. (#212)
Moving gen_random function to session.cpp. (#212)
Passing c-string (char*) representation of session id to snprintf. (#212)
Merge pull request #215 from ami-lab/f/#212-create-less-sessions

F/#212 create less sessions
Reverting back to 5% probability of cleaning up old sessions. (#212)
Merge branch 'master' of github.com:ami-lab/AmI-Platform into f/#184-compute-skeleton-joints-coordinates-fix-track_event-usage