Added the possibility to instantiate the dynSeries class from an excel (xls or xlsx) file.

Closes #348

(cherry picked from commit b7b4a9afdc4c882ee089d5d260c65b6d651c17fe)
Added unitary tests (instantiation of the dynSeries class form an excel file).

(cherry picked from commit 84075cab8196fadfab4c2be556a370be3b0bed52)