Add stats on FRAG module

[dfguerrerom]

          forgot to mention: the module GWB_FRAG in version 1.9.1 now has a new additional parameter "statistics", which can have the values: 0 (default) or 1 (add summary statistics). This parameter needs to be added in the jupyter notebook of GWB_FRAG. Its setup is identical to the "Compute  statistics" switch in the GWB_MSPA jupyter notebook, so maybe simply copy over the statistics segment from the MSPA jupyter notebook.

Originally posted by @vogtpet in #64 (comment)