_createSession = function (snapshot) {
      sessions[snapshot.session_id] = {
        startDate: snapshot.date,
        endDate: snapshot.date,
        name: snapshot.name,
        description: snapshot.description,
        id: snapshot.session_id,
        count: 1
      };
    }
Retrieve all the snapshots for a given session id, sorted by descending date order.
Returns a promise that resolves with an array of snapshots.

@param {String} sessionId
       The session id