fix: allow Sources to be in any arbitrary directory

Allow Sources to be in any arbitrary directory. Therefore, we can have a central installation of DiCoExpress that used in parallel in different projects (same version of DiCoExpress).

Load the Load_Functions script with the following command:

source(paste0(PATH_TO_DICOEXPRESS_SOURCES, "/Load_Functions.R"), chdir = TRUE) Load_Functions()

@marie_laure.martin-magniette : Do not hesitate to contact me in case of need.