Convert the `po2json` script into a webpack plugin, and integrate the
(now trivial) po.empty.js template.
This is the last step for building the entire dist/ directory with
`npm run build` (i.e. a tool that web developers are familiar with),
and not having a split webpack+make toolchain any more.
`this.po` is not being used anywhere, so drop the whole `!loaded` code
path. There is no defer mechanism, so `po.js` *must* be loaded after
cockpit.js. Let's trigger a crash instead of silently dropping
translations, to make such a bug obvious in manual and automatic tests.
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
