Thread model and UI improvements

Adds thread model/collection for managing conversation-level state, such
as unreadCounts, group membership, thread order, etc... plus various UI
improvements enabled by thread model, including an improved compose
flow, and thread-destroy button.

Adds Whisper.notify for presenting messages to the user in an orderly
fashion. Currently using a growl-style fade in/out effect.

Also some housekeeping:
Cut up views into separate files.
Partial fix for formatTimestamp.
Tweaked buttons and other styles.

js/views/message.js

@@ -0,0 +1,64 @@
+var Whisper = Whisper || {};
+
+(function () {
+  'use strict';
+
+  var Destroyer = Backbone.View.extend({
+    tagName: 'button',
+    className: 'btn btn-square btn-sm',
+    initialize: function() {
+      this.$el.html('×');
+      this.listenTo(this.$el, 'click', this.model.destroy);
+    }
+  });
+
+  Whisper.MessageView = Backbone.View.extend({
+    tagName:   "li",
+    className: "message",
+
+    initialize: function() {
+      this.$el.
+        append($('<div class="bubble">').
+          append(
+            $('<span class="message-text">'),
+            $('<span class="message-attachment">'),
+            $('<span class="metadata">')
+          )
+        );
+      this.$el.addClass(this.model.get('type'));
+      this.listenTo(this.model, 'change', this.render); // auto update
+      this.listenTo(this.model, 'destroy', this.remove); // auto update
+    },
+
+    render: function() {
+      this.$el.find('.message-text').text(this.model.get('body'));
+      var attachments = this.model.get('attachments');
+      if (attachments) {
+        for (var i = 0; i < attachments.length; i++)
+          this.$el.find('.message-attachment').append('<img src="' + attachments[i] + '" />');
+      }
+
+      this.$el.find('.metadata').text(this.formatTimestamp());
+      return this;
+    },
+
+    remove: function() {
+      this.$el.remove();
+    },
+
+    formatTimestamp: function() {
+      var timestamp = this.model.get('timestamp');
+      var now = new Date().getTime();
+      var date = new Date();
+      date.setTime(timestamp*1000);
+      if (now - timestamp > 60*60*24*7) {
+        return date.toLocaleDateString('en-US',{month: 'short', day: 'numeric'});
+      }
+      if (now - timestamp > 60*60*24) {
+        return date.toLocaleDateString('en-US',{weekday: 'short'});
+      }
+      return date.toTimeString();
+    }
+  });
+
+})();