feat: gradebook main container classname (#228)

Co-authored-by: vlasovmichael <mykhailo.vlasov@raccoongang.com>

src/components/WithSidebar/__snapshots__/test.jsx.snap

@@ -2,7 +2,7 @@
 
 exports[`WithSidebar Component snapshots basic snapshot 1`] = `
 <div
-  className="d-flex sidebar-container"
+  className="d-flex sidebar-container page-gradebook"
 >
   <aside
     className="sidebar-class-names"

src/components/WithSidebar/index.jsx

@@ -32,7 +32,7 @@ export class WithSidebar extends React.Component {
 
   render() {
     return (
-      <div className="d-flex sidebar-container">
+      <div className="d-flex sidebar-container page-gradebook">
         <aside className={this.sidebarClassNames} onTransitionEnd={this.props.handleSlideDone}>
           { this.props.sidebar }
         </aside>