Split R package into 'dataPrepReportingGrofwild' and 'reportingGrofwild'

[mvarewyck]

Current code contains both pre-processing functions for the data and code for the web application. On the long-term:

• extract code in separate R package for pre-processing data
• include check/test functions when updating the raw/source data
• both R packages can live in the same GIT repository (separate folders)
• inform Sander on how to update pre-processing scripts backoffice