Add helpers to the Inventory model for reporting purpose
For reporting purposes, the prefix of the helpers must be Report_helperName
Helpers:
- Pedigree of the accession. Accession_pedigree.description
- Country of origin. Accession_source.geography.country_code
- Crop name: Crop.name
- Name of the inventory. Accession_inv_name.plant_name. For this case, if the inventory doesn't have a name associated, the inventory_id to be use must be the system inventory of the accession. if the user wants a specific name, he must specified the category_code and plant_name_rank.