Ellipsize long conversation window titles

Fixes #304

stylesheets/_conversation.scss

@@ -4,7 +4,11 @@
   }
 
   .conversation-title {
+    display: block;
     line-height: $header-height;
+    white-space: nowrap;
+    overflow: hidden;
+    text-overflow: ellipsis;
   }
 
   #header {

stylesheets/manifest.css

@@ -431,7 +431,11 @@ input.search {
 .conversation .file-input .close {
   top: -10px; }
 .conversation .conversation-title {
-  line-height: 36px; }
+  display: block;
+  line-height: 36px;
+  white-space: nowrap;
+  overflow: hidden;
+  text-overflow: ellipsis; }
 .conversation #header {
   position: inherit; }
 .conversation .discussion-container {