Move _errors Sass from main to base

That way errors are automatically styled on all other apps (Flamenco, Attract...)

src/styles/main.sass

@@ -2,14 +2,15 @@
 @import _config
 @import _utils
 
-@import _comments
+/* Generic styles (comments, notifications, etc) come from base.css */
+
+/* Blender Cloud specific styles */
 @import _project
 @import _project-sharing
 @import _project-dashboard
 @import _user
 @import _join
 @import _homepage
-@import _error
 @import _stats
 @import _search