Change input file formats and input paths in `chilled`

This PR changes the input archetype files within CHILLED (message_ix_buildings.data.chilled) from Excel form to CSV files.

Having them be CSVs will allow for easier tracking, and in the end nothing about them requires the use of Excel spreadsheets.

Included in this PR:

Changed the input archetype files from Excel to CSV
Fix #31 by creating a function that sets user-specific paths instead of calling it through Config
Small update to logger
Add extra file to save in post processing

iiasa / message-ix-buildings