MC-943: Grouping content blocks and containers in the Panel

- add scrollable panel in full screen
- style elements to not block eachother

Author: anthoula

app/code/Magento/PageBuilder/view/adminhtml/web/css/source/_page-builder.less

@@ -48,8 +48,14 @@
 
             .pagebuilder-panel {
                 height: 100vh;
+                overflow-y: auto;
+
+                .pagebuilder-panel-groups {
+                    padding-bottom: 41px;
+                }
 
                 .panel-controls {
+                    background-color: @color-very-dark-grayish-orange;
                     bottom: 0;
                     position: absolute;
                     width: 100%;