Remove Phrase integration + references

[shawnbot]

This PR removes the Phrase integration (and the general ability to overload the i18n render option with a JSON URL). Broadly speaking, this undoes many of the changes in #64 and gets us back to just having English "keys" in our translation objects:

// our template:
ctx.t(ctx.component.label)
// our translations:
{
  es: {
    Hi: 'Hola'
  }
}

...rather than the more verbose {component}.{path} identifiers with English translations:

// our template:
ctx.t([`${ctx.component.key}.label`, ctx.component.label])
// our translations:
{
  en: {
    'hello.label': 'Hi'
  },
  es: {
    'hello.label': 'Hola'
  }
}

...which, because we can't manipulate every call to t() within formio.js, often required hacky workarounds like "aliasing" the English keys to the abstract identifiers:

// formio.js:
this.t(component.validate.customMessage, { component })
// our translations:
{
  en: {
    'hello.validate.customMessage': 'Say hello',
    'Please say hello': '$t(hello.label)'
  },
  es: {
    'hello.validate.customMessage': 'Digame "hola"'
  }
}

Here are some of the more specific things I've done:

• I deleted all references to the ctx.tk('suffix') theme-specific template helper, which was making our templates easier to read but also causing issues in nested forms (see: #203). The templates now use ctx.t(ctx.component[path]) calls.
• I brought in i18next-parser to extract strings from the formio.js source code so that we have a more up-to-date list of strings passed to the i18next.t() method, and ran it to get all of the strings into our JSON files.
• I added a babel preval macro build step for the translations to remove entries that have no value, which allows us to keep these keys in our source code without breaking forms (because formio.js treats the empty string as "valid").

• I reworked the bits that handle embedded translations—which need docs!—so that they work without the component key abstraction. This will now display the Spanish label, regardless of the value of the English label:

  Formio.createForm({
    components: [{
      type: 'textfield',
      label: 'Your name',
      properties: {
        'es:label': 'Su nombre y apellido'
      }
    }]
  }, { language: 'es' })

  ...which makes it possible for us to start embedding translations in our shared components.

I also updated the translation docs, which you can read here and here. (Note: I have not tested these changes to the autocomplete component.)

[github-actions[bot]]

Size Change: -3.71 kB (-4%)

Total Size: 85.6 kB

Filename	Size	Change
dist/formio-sfds.standalone.js	64.9 kB	-3.71 kB (-5%)	✅

ℹ️ View Unchanged

| Filename | Size | | :--- | :---: | | `dist/formio-sfds.css` | 14 kB | | `dist/portal.js` | 6.65 kB |

_{compressed-size-action}

[shawnbot]

I'm closing this because we probably won't need to do it before the big transition to something else.