#40 Curation stats

[Proposal 521](https://pioneer.joystreamstats.live/#/proposals/521) requests: - the ability to automatically display information about changing dataDirectory daily from block #717987 (05/26/2021) to any block - the ability to view information about all curators and Leads in any specified period - the ability to estimate payments for each employee (current or former) in tJOY and USD (using the exchange rate at the time of payment) Reward relationships need to be fetched live (frontend) or cached ([API](https://api.joystreamstats.live/api/v1)). There is a related task to show salaries on jstats: https://git.joystreamstats.live/Operations/process/issues/34 For changes to Channels and Videos over time we need to identify which events need to be processed ([API](https://api.joystreamstats.live/api/v1)) to create a summary. For the time being dapplooker can be of help: http://joy.dapplooker.com/