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