move common overlay and popover css to static directory

src/app/window.coffee

@@ -112,6 +112,8 @@ window.startup()
 
 requireStylesheet 'reset.css'
 requireStylesheet 'atom.css'
+requireStylesheet 'overlay.css'
+requireStylesheet 'popover-list.css'
 
 if nativeStylesheetPath = require.resolve("#{platform}.css")
   requireStylesheet(nativeStylesheetPath)

themes/atom-dark-ui/package.json

@@ -6,13 +6,11 @@
     "select-list.css",
     "tree-view.css",
     "tabs.css",
-    "overlay.css",
     "status-bar.css",
     "markdown-preview.css",
     "fuzzy-finder.css",
     "command-panel.css",
     "command-logger.css",
-    "popover-list.css",
     "notification.css"
   ]
 }