Render proper atom-panels as children of containers

spec/panel-container-element-spec.coffee

@@ -50,6 +50,8 @@ describe "PanelContainerElement", ->
       container.addPanel(panel1)
       expect(element.childNodes.length).toBe 1
 
+      expect(element.childNodes[0].tagName).toBe 'ATOM-PANEL'
+
       panel2 = new Panel({viewRegistry, item: new TestPanelItem(), orientation: 'left'})
       container.addPanel(panel2)
       expect(element.childNodes.length).toBe 2

src/panel-element.coffee

@@ -7,7 +7,7 @@ class PanelElement extends HTMLElement
   getModel: -> @model
 
   setModel: (@model) ->
-    @appendChild(@model.getView())
+    @appendChild(@model.getItemView())
     @subscriptions.add @model.onDidDestroy(@destroyed.bind(this))
 
   destroyed: ->

src/panel.coffee

@@ -9,7 +9,9 @@ class Panel
   destroy: ->
     @emitter.emit 'did-destroy', this
 
-  getView: -> @viewRegistry.getView(@item)
+  getView: -> @viewRegistry.getView(this)
+
+  getItemView: -> @viewRegistry.getView(@item)
 
   ###
   Section: Event Subscription