Column empty and not being processed when top row's cell is empty

[jaycoolslm]

Ref #593

Describe the bug
Column is not being pulled through into dataframe
When uploading an excel which has the topmost row empty for a given column, that column will not come throw

To Reproduce
Steps to reproduce the behavior:

1. Create an excel which has headers and the top most row for column X is empty
2. dfd.readExcel
3. console.log(df.columns)
4. See column missing

Expected behavior
The column should be there

Desktop (please complete the following information):

• OS: MacOS
• Browser Safari
• Version 1.1.2

[jaycoolslm]

This is likely to be an issue with https://docs.sheetjs.com/docs/api/parse-options/

[jaycoolslm]

This can be resolved on the sheetjs level using this solution

https://stackoverflow.com/a/66859139

Danfo team - I would suggest extending the current ExcelInputOptionsBrowser object to include an object that can be spread out as args when calling this function

utils.sheet_to_json(worksheet)

I will raise a PR for this if I have time

PS: my current working implementation:

// parse excel using XLSX
    const arrBuf = await file.arrayBuffer();
		const arrBufInt8 = new Uint8Array(arrBuf);
		const workbook = XLSX.read(arrBufInt8, { type: 'array' });
		const worksheet = workbook.Sheets[workbook.SheetNames[0]];
		const data = XLSX.utils.sheet_to_json(worksheet, { defval: '' });
		// instantiate new dataframe
    let df = new dfd.DataFrame(data)