CMS-4357 Implement User Manager TreeGrid - part1- edited

1. Folders GROUPS, ROLES, USERS added for all Userstores
2. fetch users from userstore - implemented
3. UserTreeGridItemViewer.ts  used icon class for showing items in BrowsePanel
4. but ItemSelection panel still  used png files from   the resources\web\admin\common\images\icons
 so need to change this behavior, I talked with Pavel an he said, that need to create a new task for this issue.
 api.app.BrowseItem and BrowsePanel.treeNodesToBrowseItems() should be refactored