Fixing issues:
#72 (closed): Flagging when using dense error matrix without 4M-GVO (Bug)
#70 (closed): Possibility to export data at every analysis step (QoL)
#71 (closed): Shifting forecast and analysis times to match that of observations (Bug)
#74 (closed): Warning the user when dealing with 4M-GVO before SWARM era (QoL)
#79 (closed) #82 (closed): Backward scheme for the last analysis (enabled through last_analysis_backward keyword in configuration file, default is True) (New feature)