Stop page extending out of viewport width by 40px

Currently the .container and .wrapper-footer elements are set to 100%,
and also have horizontal padding added to them. This results in a total
width of greater than the full width of the viewport; This causing the
browser to scroll horizonally into empty space, regardless of how wide
the viewport is.

I had added the `box-sizing: border-box` to these elements in order to
resolve this.

Cheers,
Louis

lms/static/sass/base/_base.scss

@@ -107,6 +107,7 @@ a:focus {
 
 .container {
   @include clearfix;
+  box-sizing: border-box;
   margin: 0 auto 0;
   padding: 0px 30px;
   max-width: grid-width(12);

lms/static/sass/shared/_footer.scss

@@ -8,6 +8,7 @@
 
   footer {
     @include clearfix();
+    box-sizing: border-box;
     max-width: grid-width(12);
     min-width: 760px;
     width: flex-grid(12);