[NWD] Fix EPPlus loading issue with certain spreadsheets.

ExcelPackage.Workbook was being accessed before it was initialized; this
change just passes the workbook to the constructor of the classes that
need it.

Change-Id: I7ebd4dfe02011ab117ecffc35168f0b2066ccfdf
Reviewed-on: https://gnocchi-internal-review.git.corp.google.com/c/third_party/epplus/+/207700
Reviewed-by: Hughes Hilton <hugheshilton@google.com>