[IMP] add a button on kanban to open child partner

[clementmbr]

Add a subtle external link button on child partner kanban to open it completely :

The breadcrumb is not very consistent. Sometimes it adds an intermediary "Contacts" sometimes it reset to main "Contacts" action :

... But it is still much less pain than to be blocked when you only want to open quickly the child and you can't. cc @rvalyi @alexis-via

[clementmbr]

I've just noticed that I forgot the mandatory dependency on module "contacts"... Is it still a PR for this repo ? Or should I create a mini module just for this ?