Improve tracks CRUD

* Add index, edit and update action;
* Add _form partial;
* Add link to tracks/index in nav;
* Refactor specs.

app/controllers/tracks_controller.rb

@@ -1,4 +1,8 @@
 class TracksController < ApplicationController
+  def index
+    @tracks = Track.all
+  end
+
   def show
     @track = Track.find(params[:id])
   end
@@ -7,6 +11,10 @@ class TracksController < ApplicationController
     @track = Track.new
   end
 
+  def edit
+    @track = Track.find(params[:id])
+  end
+
   def create
     @track = Track.new(track_params)
 
@@ -17,6 +25,17 @@ class TracksController < ApplicationController
     end
   end
 
+  def update
+    @track = Track.find(params[:id])
+
+    if @track.update_attributes track_params
+      redirect_to action: :index
+    else
+      render :edit
+    end
+  end
+
+
   private
 
   def track_params