Reverse the loading order of themes.

We want the first/top-most theme's css to be loaded after the others 
so its styles will override styles in the other themes.

src/theme-manager.coffee

@@ -39,6 +39,11 @@ class ThemeManager
     config.observe 'core.themes', (themeNames) =>
       @unload()
       themeNames = [themeNames] unless _.isArray(themeNames)
+
+      # Reverse so the first (top) theme is loaded after the others. We want
+      # the first/top theme to override later themes in the stack.
+      (themeNames = _.clone(themeNames)).reverse()
+
       @activateTheme(themeName) for themeName in themeNames
       @loadUserStylesheet()