Implement playlist edit feature

* Display playlists as links in index
* Move playlist form in a partial

app/views/playlists/_form.html.haml

@@ -0,0 +1,4 @@
+= form_for @playlist do |f|
+  = f.label :name
+  = f.text_field :name
+  = f.submit submit_text

app/views/playlists/edit.html.haml

@@ -0,0 +1 @@
+= render 'form', :submit_text => 'Save'

app/views/playlists/index.html.haml

@@ -1,4 +1,5 @@
 = link_to 'Create playlist', new_playlist_path
 %ul
   - @playlists.each do |p|
-    %li= p.name
+    %li
+      = link_to p.name, edit_playlist_path(p)

app/views/playlists/new.html.haml

@@ -1,4 +1 @@
-= form_for @playlist do |f|
-  = f.label :name
-  = f.text_field :name
-  = f.submit 'Create'
+= render 'form', :submit_text => 'Create'