Add Pane.moveItem(item, index)

This is the precursor to supporting drag/drop of tabs within and
between panes.

spec/app/pane-spec.coffee

@@ -128,6 +128,29 @@ describe "Pane", ->
         pane.removeItem(editSession2)
         expect(editSession2.destroyed).toBeTruthy()
 
+  describe ".moveItem(item, index)", ->
+    it "moves the item to the given index and emits a 'pane:item-moved' event with the item and the new index", ->
+      itemMovedHandler = jasmine.createSpy("itemMovedHandler")
+      pane.on 'pane:item-moved', itemMovedHandler
+
+      pane.moveItem(view1, 2)
+      expect(pane.getItems()).toEqual [editSession1, view2, view1, editSession2]
+      expect(itemMovedHandler).toHaveBeenCalled()
+      expect(itemMovedHandler.argsForCall[0][1..2]).toEqual [view1, 2]
+      itemMovedHandler.reset()
+
+      pane.moveItem(editSession1, 3)
+      expect(pane.getItems()).toEqual [view2, view1, editSession2, editSession1]
+      expect(itemMovedHandler).toHaveBeenCalled()
+      expect(itemMovedHandler.argsForCall[0][1..2]).toEqual [editSession1, 3]
+      itemMovedHandler.reset()
+
+      pane.moveItem(editSession1, 1)
+      expect(pane.getItems()).toEqual [view2, editSession1, view1, editSession2]
+      expect(itemMovedHandler).toHaveBeenCalled()
+      expect(itemMovedHandler.argsForCall[0][1..2]).toEqual [editSession1, 1]
+      itemMovedHandler.reset()
+
   describe "core:close", ->
     it "removes the active item and does not bubble the event", ->
       containerCloseHandler = jasmine.createSpy("containerCloseHandler")

src/app/pane.coffee

@@ -104,6 +104,12 @@ class Pane extends View
     @trigger 'pane:item-removed', [item, index]
     @remove() unless @items.length
 
+  moveItem: (item, newIndex) ->
+    oldIndex = @items.indexOf(item)
+    @items.splice(oldIndex, 1)
+    @items.splice(newIndex, 0, item)
+    @trigger 'pane:item-moved', [item, newIndex]
+
   itemForPath: (path) ->
     _.detect @items, (item) -> item.getPath?() is path