Global option to show account username

[zxcat]

There lot of places where account name displayed. Originally accounts moved from Golos, which is now dApp. So account names displayed along with username in golos domain.
But there are new dapps and new accounts created, which is not related to Golos.

It will be useful to allow explorer user to set preferred domains (or set none), from which to fetch usernames of accounts.

[zxcat]

requires #119