Fixed wrong behavior with down-payment invoices / credit notes of DPI:
- No more on the fly line item generation
- These documents line item is now flagged as "translatable" and is hold as-is with its translation context on the database
Removed no more used duplicate method
Merge branch 'feature/translatable_line_items' into develop

Conflicts:
	www/invoicing/api/doc.py
	www/invoicing/api/resources/embedded/invoice_item.py
	www/invoicing/models/embedded/invoice_revision.py
Fix HTML entities escaping on HTML parser
Added missing formatters for invoice and credit note PDF generators
Merge branch 'develop' of github.com:Naeka/vosae-app into develop