New: Add number of product in stock before and after selected period
when a filter is done on a period + a specific product.

Conflicts:
	htdocs/langs/en_US/stocks.lang
	htdocs/langs/fr_FR/stocks.lang
	htdocs/product/stock/mouvement.php

Conflicts:
	htdocs/langs/en_US/stocks.lang
	htdocs/langs/fr_FR/stocks.lang