feat: implement burning of slashed collateral (WIP0023)
I made all relevant Tally tests conditional on WIP0023 being activated. I could not find a proper way of enabling all tests with a new WIP being activated, so I added a temporary placeholder in wip_info() and test_wip_info(). If you uncomment those, you can verify all tests pass with and without WIP0023 being active.
I was not sure if I should just update the WIP in initialize_wip_information() nor the associated tests, but for now I did.
I have changed the base of this PR from master to witnet-1.6 so that it can be merged at any time without disrupting any further planned or unplanned 1.5.x releases from master.
This is now on 1.6 and on its road to master in #2354