Revise newsletter component

[stephaniehobson]

Like the proposed block component (#326) it'd be nice if the newsletter component had vertical alignment modifier classes. Not all newsletter images are created the same.

These should match whatever we decide on in #360.

Examples:

[craigcook]

We should revamp the newsletter component to be more layout-agnostic, the side-by-side can now be achieved with the Split component so we should just focus on the form itself.