Revise *status help output

Make it possible to output help for given command(s) and align
casing & arguments in general help & command specific usage output.
Revise *controlpanel help output

Make the output easier to read by wrapping mandatory argument names
with angle brackets (just like in *status help), and make it possible
to output help for given command(s). Furthermore, output only relevant
variable lists and align casing & arguments in general help & command
specific usage output.
Merge pull request #629 from jpnurmi/help

Revise *status and *controlpanel help output
Web: make the banner logo a link to home
webadmin: cleanup unused variables
webadmin: add missing page title

Makes sure "Traffic Info" shows up in the breadcrumbs.
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 leads to less clutter in the sidebar.
webadmin: tweak settings

Replaced the welcome page greeting with user's own settings,
renamed "Global Settings" to "Configuration", and reorganized
the sidebar.