Can't add relative timelocks (nSequence field) to transaction using the playground

[rkalis]

This issue was raised on the old playground repo by @mr-zwets (CashScript/cashscript-playground-old#15).

You can't add relative timelocks (nSequence field) to transaction using the playground. Because of this it's not possible to make transactions with the Licho's Mecenas# example smart contract in the playground.