add Excel data loading

[RandomFractals]

use SheetJS library for loading Excel files: https://github.com/SheetJS/sheetjs

See this Excel data provider for sample usage:

https://github.com/RandomFractals/vscode-data-preview/blob/master/src/data.providers/excel.data.provider.ts

Test use case scenario:

1. Create Excel file with USA state capitals, airports and zipcodes
2. Load a kepler.gl map from usa.xlsb to view those 3 point and polygon layers in one go.