Allow panes to have model objects as items in addition to views

The problem I've been struggling with is that we need to potentially 
assign tabs both to EditSessions and also to other views added by
extensions, like a markdown preview view. EditSessions are however not
actually views… instead they plug into editors. The solution is to
have the pane ask a model object what view should be used to render
it. When asked to show a non-view item, the pane constructs and
appends a view for that item or recycles an appropriate view that it
has already appended.

src/app/edit-session.coffee

@@ -52,6 +52,9 @@ class EditSession
     @subscribe @displayBuffer, "changed", (e) =>
       @trigger 'screen-lines-changed', e
 
+  getViewClass: ->
+    require 'editor'
+
   destroy: ->
     throw new Error("Edit session already destroyed") if @destroyed
     @destroyed = true

src/app/editor.coffee

@@ -66,7 +66,12 @@ class Editor extends View
     editor.isFocused = state.isFocused
     editor
 
-  initialize: ({editSession, @mini, deserializing} = {}) ->
+  initialize: (editSessionOrOptions) ->
+    if editSessionOrOptions instanceof EditSession
+      editSession = editSessionOrOptions
+    else
+      {editSession, @mini, deserializing} = (options ? {})
+
     requireStylesheet 'editor.css'
 
     @id = Editor.nextEditorId++
@@ -485,6 +490,9 @@ class Editor extends View
     index = @pushEditSession(editSession) if index == -1
     @setActiveEditSessionIndex(index)
 
+  setModel: (editSession) ->
+    @edit(editSession)
+
   pushEditSession: (editSession) ->
     index = @editSessions.length
     @editSessions.push(editSession)

src/app/pane.coffee

@@ -1,4 +1,5 @@
 {View} = require 'space-pen'
+$ = require 'jquery'
 PaneRow = require 'pane-row'
 PaneColumn = require 'pane-column'
 
@@ -12,13 +13,27 @@ class Pane extends View
     new Pane(deserialize(wrappedView))
 
   initialize: (@items...) ->
-    @viewsByItem = new WeakMap
+    @viewsByClassName = {}
     @showItem(@items[0])
 
   showItem: (item) ->
     @itemViews.children().hide()
-    @itemViews.append(item) unless @itemViews.children(item).length
-    item.show()
+    view = @viewForItem(item)
+    unless view.parent().is(@itemViews)
+      @itemViews.append(view)
+    view.show()
+
+  viewForItem: (item) ->
+    if item instanceof $
+      item
+    else
+      viewClass = item.getViewClass()
+      if view = @viewsByClassName[viewClass.name]
+        view.setModel(item)
+        view
+      else
+        @viewsByClassName[viewClass.name] = new viewClass(item)
+
 
   serialize: ->
     deserializer: "Pane"