Provide z-index centralisation for lower components

client/src/app/app.component.scss

@@ -21,7 +21,7 @@
   display: flex;
 
   .top-left-block {
-    z-index: z(headerLeft);
+    z-index: 1;
     height: $header-height;
     display: flex;
     align-items: center;

client/src/app/header/search-typeahead.component.scss

@@ -30,7 +30,7 @@
 .jump-to-suggestions {
   top: 100%;
   left: 0;
-  z-index: 35;
+  z-index: z(typeahead);
   width: 100%;
 }
 

client/src/app/shared/video/video-thumbnail.component.scss

@@ -25,7 +25,7 @@
     border-radius: 3px;
     font-size: 12px;
     font-weight: $font-bold;
-    z-index: 1;
+    z-index: z(miniature);
   }
 
   .video-thumbnail-duration-overlay {

client/src/app/videos/+video-watch/video-watch.component.scss

@@ -462,6 +462,7 @@ my-video-comments {
 .privacy-concerns {
   position: fixed;
   bottom: 0;
+  z-index: z(privacymsg);
 
   padding: 5px 15px;
 

client/src/sass/include/_variables.scss

@@ -102,9 +102,10 @@ $variables: (
 /*** z-index groups ***/
 
 $zindex: (
+  miniature    :    10,
+  privacymsg   :    20,
+  typeahead    :    30,
   header       :  1000,
-  /* header context */
-  headerLeft   :    10,
   menu         : 11000,
   dropdown     : 12000,
   popover      : 13000,