Add support for translation

[jtpio]

For now user facing strings are not necessarily translated and most of them are hardcoded in English:

voila-gridstack/packages/jupyterlab-gridstack/src/editor/components/metadata.tsx

Line 67 in 9879049

<label className="col-25">Name:</label>

There could be a pass on the code base to add support for translation. That would mean adding a dependency on ITranslator and using it for user facing text, like in this example:

• https://github.com/jupyterlab/extension-examples/blob/8bc09d2839efed8078c9fbc43da0fd39a0b7d0a3/signals/src/index.ts#L55
• https://github.com/jupyterlab/extension-examples/blob/8bc09d2839efed8078c9fbc43da0fd39a0b7d0a3/signals/src/index.ts#L81