webadmin: tweak settings

Replace "your settings" with username-link, and rename "global settings"
to "settings". A bit less clutter in the sidebar. :)
webadmin: combine "List Users" & "Add User"

Let add users via the list of users in the similar manner it’s
done for networks. It’s evidently an extra step to add a user,
but on the other hand it gives a nice overview of the users
when adding new ones, and again, leads to less clutter in the
sidebar.
webadmin: cleanup unused variables
webadmin: add missing page title

Makes sure "Traffic Info" shows up in the breadcrumbs.