Use the i18next eslint plugin

[lslezak]

Problem

• We do not automatically scan the web UI for untranslated texts, we can easily miss some translations

Solution

• Use the eslint-plugin-i18next plugin to find all text literals in the JSX templates

Notes

• This is not a perfect solution, it reports only string literals, it cannot find cases like this:

// missing translation
const msg = "message";
...
<b>{msg}</b>

• However, it still found like a half dozen of missing translations so it still makes sense