more tab work

- only one tab for any channel can be open
- rudimentary unread indicators
- add some css

res/css/application-low-priority.css

@@ -3,6 +3,31 @@ application wide stuff
 has to be separate to allow main.css to override certain things
 */
 
+.app-window tabbar .box {
+    margin: -7px -1px -7px -1px;
+    background: #2a2a2a;
+    border: 1px solid black;
+}
+
+.app-window tabbar tab:hover {
+    box-shadow: inset 0 -7px lighter(blue);
+}
+
+.app-window tabbar tab:checked {
+    box-shadow: inset 0 -7px blue;
+}
+
+.app-window tabbar tab {
+    background: #1A1A1A;
+    border: 1px solid #808080;
+}
+
+.app-window tabbar tab.needs-attention {
+  font-weight: bold;
+  animation: 150ms ease-in;
+  background-image: radial-gradient(ellipse at bottom, #FF5370, #1A1A1A 30%);
+}
+
 .app-window label:not(:disabled) {
     color: @text_color;
 }