Call recoverTransaction and check if the user is registered

[makevoid]

We need an optional feature (can be enabled but it is disabled by default) of preventing unregistered users to submit transactions - we need registeredUsers, an array of ethereum addresses of registered users that are allowed to transact.

We can use
https://web3js.readthedocs.io/en/1.0/web3-eth-accounts.html#recovertransaction
to check which address sent the signed-transaction and we can check if the address is present in the registeredUsers array

naming: registeredUsers / registeredUserAddresses or another similar name is ok

[makevoid]

isUserRegistered(ethereumAddress)

[makevoid]

add mantle-demo code to show this

[Alaanzr]

I'll create a separate ticket/PR for the mantle-demo example of this