use atomic file creation and updates when writing sampled ensight data

Issue raised on EP2007. If, for any reason, the simulation crashes while writing out ensight data, the resulting EnSight case file will very likely reference a truncated or corrupt file (does not make ensight happy).

First change required is to support an atomic OFstream option. This would create a file with a temporary name and only rename/move it to the final location after all writing is completed. If there is a crash during writing, there will be a few temporary files kicking about, but the expected output (in this case ensight) will not be corrupt.

The next changes would involve adjusting the management of ensight case updates to ensure that only consistent states exist. For the surface writing, this would mean attaching extra behaviour to the beginTime/endTime synchronization points.