Adds currency to rich snippets

The offer will not be displayed without the iso currency. There will be collisions in currencies such as AUD CAD and USD, without the sign.

themes/default-bootstrap/product.tpl

@@ -358,6 +358,7 @@ var contentOnly = {if $content_only}true{else}false{/if}
 					<!--{if $tax_enabled  && ((isset($display_tax_label) && $display_tax_label == 1) OR !isset($display_tax_label))}
 						{if $priceDisplay == 1}{l s='tax excl.'}{else}{l s='tax incl.'}{/if}
 					{/if}-->
+				<meta itemprop="priceCurrency" content="{$currency->iso_code}" />
 				{/if}
 				</p>