Allow link releases to initiatives from other products.

Right now you can link releases to an initiative but only inside the same product.  This does not happen for features that can be linked to an initiative from another product. 

If you have a complex set up of products with transversal initiatives that affect several of them you need to be able to also link the release to initiatives from other products in :

https://www.dropbox.com/s/no5qwdvhu8n18pu/Captura%20de%20pantalla%202015-09-22%2017.58.46.png?dl=0