Description of the enhancement

Implement basic functionality of the groups view in sidebar using Vue. Part of #1704.

What new functionalities would the enhancement make possible?

Enable viewing and navigating the groups hierarchy in the UI.

Task list

• Loading and building correct tree structure when group hierarchy is not expanded (on vocab home)
• Loading and building correct tree structure when group hierarchy is expanded (on group page)
• Loading new groups/concepts into group hierarchy
• Displaying group hierarchy in UI