Fix registration date error

[arnaud-eb]

Fixes ensdomains/ens-app#1331

This PR:

• Adds method in class Registrar to query events
• Parses NameRegistered events from permanent registrar filtered by selected subdomain
• If subdomain previously registered in legacy auction-based registrar, takes block timestamp of last emitted NameRegistered event as registration date for selected subdomain

Before

After

[makoto]

An auction for this name was started in 2018, but the auction never completed. The name was first registered recently, but the manager shows a registration date in 2018.
Doesn't this pick permEntry.registrationDate, regardless of auction completed or not?

For example, apt-get.eth was one of the names registered during the auction but showing the last registered name using your PR branch (on the left).

[arnaud-eb]

Thank you! Yes, you are right. After having a closer look, I wonder if the ens manager app should even display the registration date when the auction never completed in the legacy registrar to remain consistent with current behavior of permanent registrar (i.e. registration date is not reported for names registered with permanent registrar). That could be a new feature though. Last commit resets the registration date to 0 when the auction never finalized so that the registration date does not show up. Finally, I am not sure if this validity check should be implemented in the ensdomains/ui library or in the ens manager app (getRegistrarEntry() in resolvers.js).