Snackbar Improvements

[petegivens]

1. Snackbar needs to be able to accept an action. This should probably be two props passed in: actionLabel(string) and action(function). Or maybe one action prop in the shape of ['Do Stuff', () => { // do stuff }].

2. Nice to have: It would be nice to eliminate the multiline prop. Instead, on mobile, the snackbar should detect the width of the message string and auto-determine if it should be two lines instead of one.