Renew namespace view improvements

[cryptoBeliever]

Steps to reproduce:

1. Go to namespaces view and create a new namespace.
2. Choose "Extend duration" for newly created namespace

View:

Same namespace in explorer:

Problems:

• "Expires in" block is 238443 but should be 235563. 2880 blocks is a grace period on testnet (on mainnet it's 86400). Block height should by endHeight - gracePeriod