Use dumped config of guide spreadsheets to speed up get_data

[odscjames]

Current function get data can be slow when extracting many fields.

One reason for this is the code is actually working with 2 Excel sheets at the same time, the input and the guide.

Change function so that it uses the dumped config JSON blob from #16 instead of the guide.

Now function only works with 1 Excel sheet and is hopefully much faster (we are assuming here working with an excel spreadsheet is much slower than working with a small JSON blob where all data is already in the correct format, but that is probably a safe assumption)