Build translations with webpack

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.

po/po.empty.js

@@ -1,2 +0,0 @@
-/* The syntax of this line is important for po2json */
-cockpit.locale({"":{"language":"en"}});

po/po2json

@@ -1,127 +0,0 @@
-#!/usr/bin/env node
-
-function fatal(message, code) {
-    console.log((filename || "html2po") + ": " + message);
-    process.exit(code || 1);
-}
-
-function usage() {
-    console.log("usage: po2json [--module=template.js] [--output=output.js] input");
-    process.exit(2);
-}
-
-var fs, po2json, Jed, stdio;
-
-try {
-    fs = require('fs');
-    po2json = require('po2json');
-    Jed = require('jed');
-    stdio = require('stdio');
-} catch(ex) {
-    fatal(ex.message, 127); /* missing looks for this */
-}
-
-var argi = 2;
-var filename = null;
-
-var opts = stdio.getopt({
-    module: { key: "m", args: 1, description: "Module template to include", default: "" },
-    output: { key: "o", args: 1, description: "Output file", default: "" },
-});
-
-if (!opts.args || opts.args.length != 1) {
-    usage();
-}
-
-parse();
-
-function prepareHeader(header) {
-    var body, statement, plurals = header["plural-forms"], ret = null;
-    if (plurals) {
-        try {
-            /* Check that the plural forms isn't being sneaky since we build a function here */
-            Jed.PF.parse(plurals);
-        } catch(ex) {
-            fatal("bad plural forms: " + ex.message, 1);
-        }
-
-        /* A function for the front end */
-	statement = header["plural-forms"];
-        if (statement[statement.length - 1] != ';')
-            statement += ';';
-	ret = 'function(n) {\nvar nplurals, plural;\n' + statement + '\nreturn plural;\n}';
-
-        /* Added back in later */
-        delete header["plural-forms"];
-    }
-
-    /* We don't need to be transferring this */
-    delete header["project-id-version"];
-    delete header["report-msgid-bugs-to"];
-    delete header["pot-creation-date"];
-    delete header["po-revision-date"];
-    delete header["last-translator"];
-    delete header["language-team"];
-    delete header["mime-version"];
-    delete header["content-type"];
-    delete header["content-transfer-encoding"];
-
-    return ret;
-}
-
-/* Parse and process the po data */
-function parse() {
-    filename = opts.args[0];
-    po2json.parseFile(opts.args[0], { "fuzzy": false }, function(err, jsonData) {
-        var plurals, pos;
-
-        if (err)
-            fatal(err.message);
-
-        var header = jsonData[""];
-        if (header)
-            plurals = prepareHeader(header);
-
-        var data = JSON.stringify(jsonData, null, 1);
-
-        /* We know the brace in is the location to insert our function */
-        if (plurals) {
-            pos = data.indexOf('{', 1);
-            data = data.substr(0, pos + 1) + "'plural-forms':" + String(plurals) + "," + data.substr(pos + 1);
-        }
-
-        if (data == JSON.stringify({}))
-            finish("");
-        else
-            wrap(data);
-    });
-}
-
-/* Wrap the data if desired */
-function wrap(data) {
-    if (opts.module) {
-        filename = opts.module;
-        fs.readFile(opts.module, { encoding: "utf-8" }, function(err, template) {
-            if (err)
-                fatal(err.message);
-            data = template.replace('{"":{"language":"en"}}', data);
-            finish(data);
-        });
-    } else {
-        finish(data);
-    }
-}
-
-/* Write it out */
-function finish(data) {
-    if (opts.output) {
-        fs.writeFile(opts.output, data, function(err) {
-            if (err)
-	        fatal(err.message);
-            process.exit(0);
-        });
-    } else {
-        process.stdout.write(data);
-        process.exit(0);
-    }
-}