Add option to define a computational and reference period for indices that uses data for reference.
The computation for some indices e.g., count percentile occurrences, can be costly when the bootstrapping method is used. Right now there is no way of defining the computational period for the index such that the bootstrapping method will always be used. To make it possible for the user to define both a reference period and a computational period it would enable the method to run without using the bootstrapping method.
E.g., the user have a data file with time range 2001-2100 and wants to use 2001-2031 as the reference period and 2032-2100 for the index computation. The user would then define reference period to "2001-2031" and computational period to "2032-2100". The index function then needs to check if there is any overlap between these two periods because for those years the bootstrapping method would be needed. If there is no overlap the bootstrapping method is not needed. However, defining a computational period may need other changes as well such as the output template name.