Make the page background less bright

This commit changes the "$white" variable in the default theme to
be slightly off-white, to slightly reduce contrast and brightness
of the page in general and attempt to be easier on the eyes.

It also makes `body` use this variable to determine background color.

Change-Id: I670e569eb749de1e43748cef2625d4bd76ec07d5

src/theme/base/_body.scss

@@ -18,6 +18,7 @@
  */
 
 body {
+    background-color: $white;
     margin-top: $navbar-height;
     margin-bottom: 20px;
 }

src/theme/storyboard/_bootstrap_overrides.scss

@@ -1,5 +1,5 @@
 // ============================== Custom Variables =============================
-$white: #FFFFFF;
+$white: #f7f6f4;
 $black: #000000;
 
 // ============================== Bootstrap Overrides ==========================