Put 'atom' in window title when no panes are open

Previously the title would revert to 'index.html' when
focus was gained and no panes were open.

spec/app/root-view-spec.coffee

@@ -175,10 +175,10 @@ describe "RootView", ->
           expect(rootView.title).toBe "#{item.getTitle()} - #{project.getPath()}"
 
       describe "when the last pane item is removed", ->
-        it "sets the title to the project's path", ->
+        it "update the title to contain the project's path", ->
           rootView.getActivePane().remove()
           expect(rootView.getActivePaneItem()).toBeUndefined()
-          expect(rootView.title).toBe project.getPath()
+          expect(rootView.title).toBe "atom -#{project.getPath()}"
 
       describe "when an inactive pane's item changes", ->
         it "does not update the title", ->

src/app/root-view.coffee

@@ -82,7 +82,7 @@ class RootView extends View
       @getActivePane().focus()
       false
     else
-      @setTitle(null)
+      @updateTitle()
       focusableChild = this.find("[tabindex=-1]:visible:first")
       if focusableChild.length
         focusableChild.focus()
@@ -115,7 +115,7 @@ class RootView extends View
       if item = @getActivePaneItem()
         @setTitle("#{item.getTitle?() ? 'untitled'} - #{projectPath}")
       else
-        @setTitle(projectPath)
+        @setTitle("atom - #{projectPath}")
     else
       @setTitle('untitled')