Fixup conversation page styles and functionality

Render the entire conversation from a template, because some parts of it
must be rendered conditionally if it is a group vs private conversation.

Also apply some style fixes and restore lost functionality:
  * Make conversation title bar fixed.
  * Widens message bubbles.
  * Unhide message list.
  * Restore attachment rendering.
  * Restore message sending and attachment file selection.
  * Style attachments file input as a paperclip.
  * Style send button like on Android and make it a submit input.

js/conversation_panel.js

@@ -24,7 +24,7 @@
         conversation.fetch().then(function () {
             new Whisper.ConversationView({
                 model: conversation
-            }).render().$el.appendTo($('#conversation-container'));
+            }).render().$el.prependTo($('body'));
         });
     };
 

js/views/conversation_view.js

@@ -37,7 +37,7 @@
             this.view = new Whisper.MessageListView({
                 collection: this.model.messageCollection
             });
-            $('#header').after(this.view.el);
+            this.$el.find('.discussion-container').append(this.view.el);
 
             this.model.fetchMessages({reset: true});
         },
@@ -73,7 +73,7 @@
 
         sendMessage: function(e) {
             e.preventDefault();
-            var input = this.$el.find('.send input');
+            var input = this.$el.find('.send input.send-message');
             var message = input.val();
             var convo = this.model;
 

js/views/file_input_view.js

@@ -34,7 +34,7 @@ var Whisper = Whisper || {};
 
         addThumb: function(e) {
             this.thumb.src = e.target.result;
-            this.$el.append(this.thumb.render().el);
+            this.$el.find('.paperclip').append(this.thumb.render().el);
         },
 
         previewImages: function() {