Filter sidebar menu's that user isn't privileged for

= This is a combination of 2 commits.
= This is the 1st commit message:

Atm you're redirected to /users after login even when you aren't privileged to any of the user actions. This should be addressed in a following commit.

It will only show the menu's on the left for which you are privileged. This can be depending on role (e.g. settings for admin) or privilege (e.g. user actions).

= This is the 2nd commit message:

It will only show the menu's on the left for which you are privileged. This is depending on privileges.

The redirect for root is now also set after login before adding the route.
That way we can set the route to the path corresponding with the first item in the sidebar.
When there's no unhidden route (e.g. when admin-fe doesn't know about any privilege the user has), the redirect goes to /401.