* Fixed es.json
- converted remaining english to spanish in file so as to check more locations.
- the `formatjs compile` for Spanish was failing converted back to english for now. build does the correct thing, so it's more just to keep things correct in source.
* add support for eslint-plugin-formatjs
- eslint rules for formatjs
- we are mostly protected by typescript checking, but this is a nice sanity check.
* End-to-end localization working
* Update package.json
* fix FormattedMessage confusion by using the `FormattedMessage` from `gatsby-plugin-intl` NOT `react-intl`
* TODO: `client/src/intl/es.json` should be generated from a translation tool.
* Update package-lock.json
Integrate gatsby-plugin-intl for internationalization
Replaces static text with `intl.formatMessage` call and Links with `gatsby-plugin-intl` equivalent
Note: `npm install` now requires `--force` to install the latest `gatsby-plugin-intl` as it doesn't explicitly support gatsby3.0
