Add 2020 Q3 financial transparency report, update old reports to account for tx fees

[lehnberg]

This PR replaces https://github.com/mimblewimble/grin-pm/pull/362

It:

• Adds tx fee field to spending log
• Improves how spending logs account for consolidation that took place in 2019
• Fixes some minor bugs in logs and reports
• Adds a BTC 0.01744541 discrepancy in Q4 2019 to account for a mismatch in our data. This was roughly USD 125 at the time, and numbers do not add up without it. Likely this is related to how we were handling transaction outputs prior to this consolidation effort.
• Adds Q32020 transparency report

Q4 2020 report to follow in a separate PR once this has been merged.