Remove sortable list class

Because sortable list was only being used by tab bar view, I got rid
of the class hierarchy.

src/app/sortable-list.coffee

@@ -1,62 +0,0 @@
-{View} = require 'space-pen'
-$ = require 'jquery'
-
-module.exports =
-class SortableList extends View
-  @viewClass: -> 'sortable-list'
-
-  initialize: ->
-    @on 'dragstart', '.sortable', @onDragStart
-    @on 'dragend', '.sortable', @onDragEnd
-    @on 'dragover', @onDragOver
-    @on 'drop', @onDrop
-
-  onDragStart: (event) =>
-    unless @shouldAllowDrag(event)
-      event.preventDefault()
-      return
-
-    el = $(event.target).closest('.sortable')
-    el.addClass 'is-dragging'
-    event.originalEvent.dataTransfer.setData 'sortable-index', el.index()
-
-  onDragEnd: (event) =>
-    @find(".is-dragging").removeClass 'is-dragging'
-
-  onDragOver: (event) =>
-    event.preventDefault()
-    currentDropTargetIndex = @find(".is-drop-target").index()
-    newDropTargetIndex = @getDropTargetIndex(event)
-
-    if newDropTargetIndex != currentDropTargetIndex
-      @children().removeClass 'is-drop-target drop-target-is-after'
-      sortableObjects = @find(".sortable")
-      if newDropTargetIndex < sortableObjects.length
-        sortableObjects.eq(newDropTargetIndex).addClass 'is-drop-target'
-      else
-        sortableObjects.eq(newDropTargetIndex - 1).addClass 'drop-target-is-after'
-
-  onDrop: (event) =>
-    return false if !@shouldAllowDrop(event)
-    event.stopPropagation()
-    @children('.is-drop-target').removeClass 'is-drop-target'
-    @children('.drop-target-is-after').removeClass 'drop-target-is-after'
-
-  shouldAllowDrag: (event) ->
-    true
-
-  shouldAllowDrop: (event) ->
-    true
-
-  getDropTargetIndex: (event) ->
-    el = $(event.target).closest('.sortable')
-    el = $(event.target).find('.sortable').last()  if el.length == 0
-
-    elementCenter = el.offset().left + el.width() / 2
-
-    if event.originalEvent.pageX < elementCenter
-      el.index()
-    else if el.next().length > 0
-      el.next().index()
-    else
-      el.index() + 1