Move theme import right after variables import

Since the theme Sass is just a simple variables overrides (for the
moment), it must be imported right after the default variables Sass
file (if at all). At the bottom of the file, it has no effect.

lms/static/sass/application.scss.mako

@@ -4,6 +4,20 @@
 @import 'base/font_face';
 @import 'base/mixins';
 @import 'base/variables';
+
+## THEMING
+## -------
+## Set up this file to import an edX theme library if the environment
+## indicates that a theme should be used. The assumption is that the
+## theme resides outside of this main edX repository, in a directory
+## called themes/<theme-name>/, with its base Sass file in
+## themes/<theme-name>/static/sass/_<theme-name>.scss. That one entry
+## point can be used to @import in as many other things as needed.
+% if env.get('THEME_NAME') is not None:
+  // import theme's Sass overrides
+  @import '${env.get('THEME_NAME')}';
+% endif
+
 @import 'base/base';
 @import 'base/extends';
 @import 'base/animations';
@@ -36,16 +50,3 @@
 @import 'news';
 
 @import 'shame';
-
-## THEMING
-## -------
-## Set up this file to import an edX theme library if the environment
-## indicates that a theme should be used. The assumption is that the
-## theme resides outside of this main edX repository, in a directory
-## called themes/<theme-name>/, with its base Sass file in
-## themes/<theme-name>/static/sass/_<theme-name>.scss. That one entry
-## point can be used to @import in as many other things as needed.
-% if env.get('THEME_NAME') is not None:
-  // import theme's Sass overrides
-  @import '${env.get('THEME_NAME')}'
-% endif