The output file is an option, not a positional argument.
`opts.args` is undefined if there are no positional arguments, so that
just calling `po/po2json` crashed with
TypeError: Cannot read property 'length' of undefined
Similarly to commit cbedf06704, provide default values, so that
`po2json po/de.po` does not error out with
Option "--module" requires 1 arguments, but 0 were provided
The current version failed with
Option "--directory" requires 1 arguments, but 0 were provided
In the current stdio npm module version, getopt() now requires a
`default:` attribute, otherwise it considers the options as required.
Also sync PO helpers with current cockpit.
Add PO template build to travis check, to make sure that it keeps
working.
Closes#375
