Add modes

[diegomura]

Currently react-portalgun does not render the component if portalType doesn't match his key value. I called this a drastic mode (name open to change).

However, we also need to support a smooth mode (again, name may/should change) that will render all portals passed, passing by a isOpen prop to each one of them. This way, the hiding logic it's up to the portal. Handy to support in/out animations and stuff like that