UPDATE: Adds web app (#79)

Things missing:

* Browse mode
* Front end tests
* Storybook

webapp/src/components/formatPicker.tsx

@@ -0,0 +1,49 @@
+import {
+  Button,
+  Dialog,
+  DialogActions,
+  DialogContent,
+  DialogTitle,
+  TextField,
+} from "@mui/material";
+import { useState } from "react";
+import { useTranslation } from "react-i18next";
+
+type FormatPickerProps = {
+  className?: string;
+  open: boolean;
+  onClose: () => void;
+  onExited?: () => void;
+  numFmt: string;
+  onChange: (numberFmt: string) => void;
+};
+
+const FormatPicker = (properties: FormatPickerProps) => {
+  const { t } = useTranslation();
+  const [formatCode, setFormatCode] = useState(properties.numFmt);
+
+  const onSubmit = (format_code: string): void => {
+    properties.onChange(format_code);
+    properties.onClose();
+  };
+  return (
+    <Dialog open={properties.open} onClose={properties.onClose}>
+      <DialogTitle>{t("num_fmt.title")}</DialogTitle>
+      <DialogContent dividers>
+        <TextField
+          defaultValue={properties.numFmt}
+          label={t("num_fmt.label")}
+          name="format_code"
+          onChange={(event) => setFormatCode(event.target.value)}
+        />
+      </DialogContent>
+      <DialogActions>
+        <Button onClick={() => onSubmit(formatCode)}>
+          {t("num_fmt.save")}
+        </Button>
+      </DialogActions>
+    </Dialog>
+  );
+};
+
+export default FormatPicker;