Fix moment locale loading in bidi support

[jcb91]

This is throwing errors like

Uncaught Error: Script error for "components/moment/locale/en-gb"
http://requirejs.org/docs/errors.html#scripterror
    at makeError (require.js?v=6da8be361b9ee26c5e721e76c6d4afce:165)
    at HTMLScriptElement.onScriptError (require.js?v=6da8be361b9ee26c5e721e76c6d4afce:1732)
makeError @ require.js?v=6da8be361b9ee26c5e721e76c6d4afce:165
onScriptError @ require.js?v=6da8be361b9ee26c5e721e76c6d4afce:1732

because of the way it's been implemented (issuing a require call to a presumed locale js file, which may not exist, especially since packaged versions of notebook are shipping with minimized moment, without the separate locale files). This PR does it in the correct way (getting moment to load it from its own internal set, if possible, also falling back to less-specific versions as necessary).

[jcb91]

Also, while looking at this, I've noticed that

• there are quite a few country-specific arabic locales (e.g. ar-sa), but the current check for whether to use the numericshaping at static/bidi/bidi.js#L29 is checking for the exact string ar, which means it'll decide not to map them. This might be intentional, but I suspect it isn't?

• moment's arabic locales already provide functions for transforming numbers in strings (see, e.g. moment/src/locale/ar-sa.js#L85-L89). Perhaps it might make more sense to use these for the numericshaping functionality than rolling new ones in notebook? This might make the above check redundant too, we could instead do something like

  var shapeNumerals = moment.localeData().postformat;
  var applyBidi = function (value) {
      return shapeNumerals(value);
  };

[takluyver]

Thanks, I don't know much about this, but this looks like an improvement to me.

cc @samarsultan and @rgbkrk (you've touched this file)

[takluyver]

I think you're right about the exact ar check, as well - it should be checking if it starts with that.

[rgbkrk]

Yeah this is much better to let moment resolve it.

It would be good to verify this with a non-English locale.

[takluyver]

I've done a brief test with an arabic locale set. I made and installed an sdist to check for packaging problems. It seemed to be working, whereas 5.2.1 installed through conda still showed me 'ago' times in English, and had the error about loading the locale.