Use columns block for the parallelogram style (#16)

This avoids the complex mutliply-nested blocks and makes the block style less reliant on a custom class. On mid-sized screens, we switch to plain horizontally-overlapping rectangles, and on small screens we stack the columns, and vertically-overlap.

Also, remove the parallelogram styles from the editor display. The skew and positioning don't work well in the editor context.

themes/wporg-5ftf/css/utilities/_utilities.scss

@@ -1,4 +1,4 @@
 @import "colors";
-@import "group";
+@import "columns";
 @import "paragraph";
 @import "pullquote";