Image manager: supported a tabbed interface on mobile

Makes interface relatively usable now on mobile sizes.
Required updating of tab handling to support tabs being active at only
mobile screen sizes, include change on resize, upon support for
potentially nested tab usage.
Tab component will now search within sensible depths for finding its own
tabs and panels to control.

resources/sass/_components.scss

@@ -380,6 +380,12 @@ body.flexbox-support #entity-selector-wrap .popup-body .form-group {
     background-color: #FFF;
   }
 }
+
+@include smaller-than($s) {
+  .image-manager-filter-bar .contained-search-box input {
+    width: 180px;
+  }
+}
 .image-manager-filters {
   box-shadow: $bs-med;
   border-radius: 4px;
@@ -475,6 +481,7 @@ body.flexbox-support #entity-selector-wrap .popup-body .form-group {
 
 .image-manager-sidebar {
   width: 300px;
+  margin: 0 auto;
   overflow-y: auto;
   overflow-x: hidden;
   border-inline-start: 1px solid #DDD;
@@ -500,6 +507,11 @@ body.flexbox-support #entity-selector-wrap .popup-body .form-group {
     }
   }
 }
+@include smaller-than($m) {
+  .image-manager-sidebar {
+    border-inline-start: 0;
+  }
+}
 
 .image-manager-content {
   display: flex;

resources/sass/_layout.scss

@@ -298,6 +298,10 @@ body.flexbox {
   }
 }
 
+[hidden] {
+  display: none !important;
+}
+
 /**
  * Border radiuses
  */