Backbone message storage and views

Adds Backbone-based Whisper.Messages model/collection with local storage
extension. Saves sent and received messages in Whisper.Messages instead
of message map. This will assign a unique id to the message and save it
to localStorage.

Adds Backbone-based view to popup.html
  Automatically updates itself when new messages are saved to
  Whisper.Messages db from the background page.

Added some shiny new styles, and started splitting up css into multiple
files for sanity's sake.

css/popup.css

@@ -0,0 +1,99 @@
+/*
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+.clearfix:before, .clearfix:after { content: "\0020"; display: block; height: 0; overflow: hidden; }
+.clearfix:after { clear: both; }
+.clearfix { zoom: 1; }
+
+body {
+  margin: 0;
+  min-width: 400px;
+  min-height: 500px;
+  font-family: sans-serif;
+  color: #333;
+}
+
+.container {
+  max-width: 960px;
+  margin: auto;
+  padding: 0 1em;
+}
+
+header {
+  padding: 5px 0;
+}
+
+form.compose {
+  position: relative;
+}
+
+label {
+  float: left;
+  margin-right: 1em;
+}
+
+form.compose input[type=text], form.compose textarea {
+  margin: 0.5em 0;
+}
+#send input[type=submit] {
+  float: right;
+}
+
+#popup_send_numbers {
+  margin-bottom: 0;
+}
+
+#popup_send_numbers:focus + .contacts,
+.contacts:hover {
+  display: block;
+  z-index: 10;
+}
+
+.contacts {
+  display: none;
+  position: absolute;
+  left: 10px;
+}
+
+.contact {
+  border: solid 1px #ccc;
+  background: #fff;
+  font-size: 88%;
+  padding-right: 5px;
+  cursor: pointer;
+}
+
+.contact .pic {
+  display: block;
+  float: left;
+  width: 30px;
+  height: 30px;
+  background: #ddd;
+}
+
+.contact .name, .contact .number {
+  line-height: 30px;
+  margin-left: 5px;
+}
+
+ul {
+  margin: 0;
+  padding: 0;
+}
+li {
+  list-style: none;
+}
+
+/* Formatting */