Update Snack Bar Component: Added Icon & Variants

[zcolah]

The material design snack bar has no icons or variants. These do not follow the best practices established in the industry. Hence I have made 4 variants - default, success, warning, and danger that indicate to a user the type of action that has taken place. In addition this I have added an icon to the snack bar to act as a signifier.

You can see the updated Snackbar in Figma here: https://www.figma.com/file/vyCg0SdVZwBElSAQ6xjwNj/DISCO-%7C%7C-Design-System?node-id=9348%3A75132

[agalin920]

@zcolah Snackbar wraps Alerts https://mui.com/material-ui/react-alert/#main-content that do have variants called 'severity' https://mui.com/material-ui/react-snackbar/

These overrides should be on Alert components

[zcolah]

@agalin920 great catch. I have updated the alert filled colors to pass accessibility tests and will be using them henceforth for our snackbars. You can see the Figma for the same here: https://www.figma.com/file/vyCg0SdVZwBElSAQ6xjwNj/DISCO-%7C%7C-Design-System?node-id=6595%3A48211