Reference templating help, add utcdate filter example

Remove "help keyword" from test Testing help output does not make sense as we have no way to check for errors in content which would be the only reasonable test here.

Refactor kwdemo and make output translatable Better reflect the actual behaviour of the extension: - Make map arguments and -f/--rcfile not mutually exclusive but extend the current configuration - Map arguments and -f/--rcfile both override the defaults even when -d/--default is specified - -d/--default only overrides the current configuration Inform the user about extending/overriding behaviour, but only at the beginning; the following messages become terser, making the output translatable without too much code clutter. Rephrase help (use "short/long" option notation etc.).