Take into account consumer price indices v1

[pierresegonne]

Improvement on #373

What is it about

EXIOBASE relies on numbers from the past. The data we're currently using is from 2011.

To improve the accuracy of our carbon equivalent numbers, we should take into account changes in prices since 2011, and then the currency exchange from 2011 as EXIOBASE is in €.

What has been done

in #373, a consumer price index (CPI) conversion was implemented:

When the amount in EUR is obtained, a CPI correction is computed with:

correctedAmountEUR = amountEUR * (currentYearCPI/referenceYearCPI) 

where currentYearCPI corresponds to the average CPI for the country (or average fallback) for the year during which the item(s) was purchased, and referenceCPI the reference CPI for the EXIOBASE (currently 2011).

As of today, only annual country CPI (COICOP agnostic) are used.

What improvements do we need

For now, the data by country is averaged over all coicop values, improving it requires:

• Add COICOPs (~4000 values)
• Potentially build a cloud function to expose this as an API as the number of values could be prohibitive

The OECD provides all relevant data.