plugin to support mcb file format

Hi,

This commit add a plugin in Gourmet recipe manager in order to import and export mcb files.
These files are the native file format for MyCookbook android recipe application (https://play.google.com/store/apps/details?id=fr.cookbook&hl=en) and MyCookbook-online web application (http://www.mycookbook-online.net/).

Can you please integrate it to gourmet ?

MyCookbook team