Some i18n support (button labels)

[vdh]

While implementing i18n, I noticed that while I could customise the labels of some of the config, the link buttons, the image button, and the history buttons (undo/redo) were still hardcoded to English values.

Here's a sample config:

const toolbarConfig = {
  // other config…
  LINK_BUTTONS: {
    link: {
      label: linkLabel,
    },
    removeLink: {
      label: removeLinkLabel,
    },
  },
  IMAGE_BUTTON: {
    label: imageButtonLabel,
  },
  HISTORY_BUTTONS: {
    undo: {
      label: undoLabel,
    },
    redo: {
      label: redoLabel,
    },
  },
};

I also replaced the deprecated react-addons-test-utils with react-test-renderer/shallow, and added react and react-dom to devDependencies so they install properly for local development.

[strongui]

Any chance of getting this merged soon?

[ArtistHam]

@sstur @sibelius Could you please add this changes to npm package?

[aleksandr-zheglov]

Are you publishing this change to npm ? It would be nice 💯