Background Overlay support

[Lara89]

New feature

Based on a boolean and possible customization, has the hability to enable a background overlay, avoiding user interaction with the background.

Some use cases:

• After saving a form
• When UX expects user to focus on toaster

[aaamenezes]

Is there a real interest of the community in this?

I feel that the overlay is more interesting to a modal, because it has a bigger content than the toast, and sometimes until as interation.

I'm starting (exactly today) in contribute to the open source projects, and I'd love to create this, but I wanna know if this feature is realy important for this project.