Move legacy (S)CSS files to legacy folder

app/assets/config/manifest.js

@@ -1,3 +1,4 @@
 //= link_tree ../images
 //= link_tree ../builds
+//= link admin.css
 //= link legacy.css

app/assets/stylesheets/admin.scss

@@ -1,4 +1,4 @@
-@import "variables";
+@import "legacy/variables";
 
 body#admin-panel {
   #wrapper {

app/assets/stylesheets/legacy.css

@@ -1,5 +1,5 @@
 /*
- * This is a manifest file that'll be compiled into application.css, which will include all the files
+ * This is a manifest file that'll be compiled into legacy.css, which will include all the files
  * listed below.
  *
  * Any CSS and SCSS file within this directory, lib/assets/stylesheets, or any plugin's
@@ -10,6 +10,6 @@
  * files in this directory. Styles in this file should be added after the last require_* statement.
  * It is generally better to create a new file per style scope.
  *
- *= require_tree .
+ *= require_tree ./legacy/
  *= require_self
  */