Clear completed & add todo at bottom of list

app/assets/javascripts/backbone/models/habit.js.coffee

@@ -9,7 +9,9 @@ class HabitTracker.Models.Habit extends Backbone.Model
     up: true
     down: true
     done: false
-    position: 0
+    # TODO this is being calculated instead on habit creation in index_view
+    # because HabitsCollection instance isn't available here.  Fix that
+    position: 0 
     
   isHabit: =>
     @get("habit_type")==1
@@ -50,10 +52,21 @@ class HabitTracker.Models.Habit extends Backbone.Model
       done = false if direction=="down"
     @set({ score: score, done: done })
     window.userStats.updateStats(this, delta)
-    
+
     #send all the update information, as well as tack on userStats which will save to Users
     @save({ user_stats: window.userStats })
     
 class HabitTracker.Collections.HabitsCollection extends Backbone.Collection
   model: HabitTracker.Models.Habit
   url: '/habits'
+  comparator: (habit) ->
+    habit.get("position")
+    
+  # Filter down the list of all todo items that are finished.
+  doneTodos: ->
+    @filter (todo) ->
+      todo.get('done') and todo.isTodo()
+
+  nextPosition: ->
+    if (!@length) then return 1
+    return @max() + 1