Use .mw-body instead of div#content

* Part of https://gerrit.wikimedia.org/r/#/c/151395/

Change-Id: Iae873906abcd8b2a986e5f728f0ce207256de770

components/animations.less

@@ -1,6 +1,6 @@
 /* Animate between standard and high definition layouts */
 body.vector-animateLayout {
-	div#content,
+	.mw-body,
 	div#footer,
 	#left-navigation {
 		.transition(margin-left 250ms, padding 250ms;);

components/common.less

@@ -27,7 +27,7 @@ body {
 }
 
 /* Content */
-div#content {
+.mw-body {
 	margin-left: 10em;
 	padding: @content-padding;
 	/* Border on top, left, and bottom side */

components/externalLinks.less

@@ -1,6 +1,6 @@
 @import "mediawiki.mixins.less";
 // External links
-#content {
+.mw-body {
 	.external {
 		background-position: center right;
 		background-repeat: no-repeat;

screen-hd.less

@@ -2,7 +2,7 @@
 
 @import "variables.less";
 
-div#content {
+.mw-body {
 	margin-left: 11em;
 	padding: 1.25em 1.5em 1.5em 1.5em;
 }