Clean up z index ordering

We have enough layers now that we need to have some system for this.
E.g. make sure that dialogs during connect show up in front of the
blocking transition layer.

app/styles/base.css

@@ -7,6 +7,20 @@
  * This file is licensed under the 2-Clause BSD license (see LICENSE.txt).
  */
 
+/*
+ * Z index layers:
+ *
+ * 0: Main screen
+ * 10: Control bar
+ * 50: Transition blocker
+ * 60: Connection popups
+ * 100: Status bar
+ * ...
+ * 1000: Javascript crash
+ * ...
+ * 10000: Max (used for polyfills)
+ */
+
 body {
   margin:0;
   padding:0;
@@ -172,6 +186,15 @@ input[type=button]:active, select:active {
   pointer-events: auto;
 }
 
+/* ----------------------------------------
+ * Layering
+ * ----------------------------------------
+ */
+
+.noVNC_connect_layer {
+  z-index: 60;
+}
+
 /* ----------------------------------------
  * Fallback error
  * ----------------------------------------
@@ -179,7 +202,7 @@ input[type=button]:active, select:active {
 
 #noVNC_fallback_error {
   position: fixed;
-  z-index: 3;
+  z-index: 1000;
   left: 50%;
   transform: translate(-50%, -50px);
   transition: 0.5s ease-in-out;
@@ -234,7 +257,7 @@ input[type=button]:active, select:active {
 #noVNC_control_bar_anchor {
   /* The anchor is needed to get z-stacking to work */
   position: fixed;
-  z-index: 2;
+  z-index: 10;
 
   transition: 0.5s ease-in-out;
 
@@ -294,7 +317,7 @@ input[type=button]:active, select:active {
   transform: translateY(35px);
   width: calc(100% + 30px);
   height: 50px;
-  z-index: -2;
+  z-index: -1;
   cursor: pointer;
   border-radius: 5px;
   background-color: rgb(83, 99, 122);
@@ -576,7 +599,7 @@ input[type=button]:active, select:active {
   top: 0;
   left: 0;
   width: 100%;
-  z-index: 3;
+  z-index: 100;
   transform: translateY(-100%);
 
   transition: 0.5s ease-in-out;
@@ -709,6 +732,8 @@ input[type=button]:active, select:active {
  */
 
 #noVNC_password_dlg {
+  position: relative;
+
   transform: translateY(-50px);
 }
 #noVNC_password_dlg.noVNC_open {
@@ -737,7 +762,7 @@ input[type=button]:active, select:active {
 
   color: white;
   background: rgba(0, 0, 0, 0.5);
-  z-index: 1000;
+  z-index: 50;
 
   /*display: flex;*/
   align-items: center;

vnc.html

@@ -272,7 +272,7 @@
     </div>
 
     <!-- Password Dialog -->
-    <div class="noVNC_center">
+    <div class="noVNC_center noVNC_connect_layer">
     <div id="noVNC_password_dlg" class="noVNC_panel">
         <ul>
             <li>