Forward window focus when active element is body

This problem was when the focus element is detached
when navigating away from the window and when
the window is then given focus again nothing has
focus.

The solution is to use RootView's focus handler
on the window to bring focus to the editor or
other view when the document's active element
is the body meaning nothing inside the RootView
currently has focus.

src/app/root-view.coffee

@@ -55,20 +55,24 @@ class RootView extends View
     panesViewState: @panes.children().view()?.serialize()
     extensionStates: @serializeExtensions()
 
-  handleEvents: ->
-    @on 'toggle-dev-tools', => atom.toggleDevTools()
-    @on 'focus', (e) =>
-      if @getActiveEditor()
-        @getActiveEditor().focus()
+  handleFocus: (e) ->
+    if @getActiveEditor()
+      @getActiveEditor().focus()
+      false
+    else
+      @setTitle(null)
+      focusableChild = this.find("[tabindex=-1]:visible:first")
+      if focusableChild.length
+        focusableChild.focus()
         false
       else
-        @setTitle(null)
-        focusableChild = this.find("[tabindex=-1]:visible:first")
-        if focusableChild.length
-          focusableChild.focus()
-          false
-        else
-          true
+        true
+
+  handleEvents: ->
+    @on 'toggle-dev-tools', => atom.toggleDevTools()
+    @on 'focus', (e) => @handleFocus(e)
+    $(window).on 'focus', (e) =>
+      @handleFocus(e) if document.activeElement is document.body
 
     @on 'active-editor-path-change', (e, path) =>
       @project.setPath(path) unless @project.getRootDirectory()