feat: add bg size, position, and parallax options to Widget Pages

#  Options are `cover` (default), `contain`, or `actual` size.
image_size = "actual"
# Options include `left`, `center` (default), or `right`.
image_position = "right"
# Use a fun parallax-like fixed background effect? true/false
image_parallax = true

See #1377

assets/sass/academic/_widgets.scss

@@ -55,15 +55,19 @@
   top: 100%;
 }*/
 
-/* Create the parallax scrolling effect */
-.parallax {
-  height: 100%;
-  background-attachment: fixed;
+/* Default background image properties for home sections. */
+.home-section.bg-image {
   background-position: center;
   background-repeat: no-repeat;
   background-size: cover;
 }
 
+/* Create a parallax-like scrolling effect. */
+.parallax {
+  height: 100%;
+  background-attachment: fixed;
+}
+
 .home-section:first-of-type {
   padding-top: 50px;
 }