[Frontend] Manual re-do of collapse/expand panes

open #90
Renamed BrowseTreeController to PaneController;
Ensuring mobile functionality parity;

platform/commonUI/general/res/sass/user-environ/_layout.scss

@@ -343,4 +343,54 @@
         @include webkitProp(flex, '1 1 0');
         padding-right: $interiorMarginLg;
     }
+}
+
+// MOVED from mobile/_layout.scss
+// When the tree is hidden, these are the
+// classes used for the left menu and the
+// right representation.
+.browse-hidetree {
+    @include user-select(none);
+    // Sets the left tree menu when the tree
+    // is hidden.
+    .pane.left.treeview {
+        opacity: 0;
+        //right: 100% !important;
+        //width: auto !important;
+        //overflow-y: hidden;
+        //overflow-x: hidden;
+    }
+    // Sets the right represenation when
+    // the tree is hidden.
+    .pane.right-repr {
+        left: 0 !important;
+    }
+}
+
+.browse-showtree {
+    // NOTE: DISABLED SELECTION
+    // Selection disabled in both panes
+    // causing cut/copy/paste menu to
+    // not appear. Should me moved in
+    // future to properly work
+    //@include user-select(none);
+
+    // Sets the left tree menu when the tree is shown.
+    .pane.left.treeview {
+        @include trans-prop-nice(opacity, .4s);
+        //@include background-image(linear-gradient(90deg, rgba(black, 0) 98%, rgba(black, 0.3) 100%));
+        opacity: 1;
+        //display: block !important;
+        //width: auto !important; // CH CO
+        //right: auto;
+        //width: $proporMenuWithView;
+    }
+    // Sets the right representation when the tree is shown.
+    .pane.right-repr {
+        //left: $proporMenuWithView;
+        //width: auto !important;
+
+        //left: 0 !important;
+        //transform: translateX($proporMenuWithView);
+    }
 }