Uniform I/O between transformers, tools and dashboard

[nightsh]

What we have now:

Target:

(draw.io link)

Tasks:

• dump everything in XLSX files
• load everything from XLSX sheets instead of individual files
• generate one file per transformer (except datajson)
• use the new files in dashboard

Acceptance criteria:

• All transformers dump in XLSX
• The name parameter will generate a new sheet, instead of a new file
• Everything works as expected, with the new data files

Note: The deprecated compare tool will be ignored for now, as well as its output. It will be subject to another task related to stats.