Move default snackbar position from centered to bottom left

[adamnel]

Describe the bug
Snackbars open centered in the window

To Reproduce

1. Visit https://teradata.github.io/covalent/docs/components/?path=/story/components-snackbar--basic
2. Click the "Toggle snackbar" button

Expected behavior
The snackbar should open 24px from the bottom left of the UI.

Screenshots