require due_date when payment_method is not blank
add hook on invoice import
add article_code and notes to invoice_lines, closes #4621
Merge branch 'master' into my_page

Conflicts:
	config/locales/ca.yml
	config/locales/da.yml
	config/locales/en.yml
	config/locales/es.yml
	config/locales/fr.yml
	config/locales/nl.yml
	config/locales/sv.yml