Snapshot board is associated with timeline. Fixing bugs in Board.load_board: - when there is no snapshot, we apply events since the start of the requested session. - strokes was not applied on snapshot./devel-run.sh  The time for message is setted by the server, not by the client. The initial snapshot of the board is removed. A play request for history does not use timestamps anymore, some events were lost, so now the client ask for max. 10 events. Client part: the current timeline id is not computed correctly.
Strokes are stored into db chronologically for each user post. Play request now returns a list of events between the requested 'since' timeline ID and the requested 'duration' (in seconds). Snapshot request doesn't returns zones without users (= leaving users).
When leaving, the removed user was not updated in the @session property, the bug was introduced when the session was stored in db and associated with users. Snapshot operation is simplified for history, and use the session start timestamp. The history uses now timestamps to request events.
Cleanup of view_session.js, switch to real_time at the end of history disabled + protection to prevent access to the end of the history.
In the slider: removing handle functions (slider is not an observer anymore), when the user wants to move the cursor, the cursor cannot be moved by set_value.
Removing console outputs in js.
Merge branch 'feature/fix-history-lost-events-light' into develop
Merge branch 'develop' into release/0.6-bhadrak
Resize the viewer canvas correctly with the slider.
Merge branch 'develop' into release/0.6-bhadrak
Merge branch 'release/0.6-bhadrak' of project.gnuside.com:poietic-generator into release/0.6-bhadrak