Improve the demo that creates a vm using ethereum

[brandonpille]

In the demo that creates a vm using ethereum we require the user to have an ethereum account, a stellar account and a tfchain account. It would be better to create the stellar account for the user and use ethereum to activate the account (because the activation requires some tokens to be transferred on the stellar account). An activation service has been created in threefoldfoundation/tft#240 allowing us to account an account by transferring some ethereum to it. We should use this activation service to create the account:

• create an api call in the ethereum client that allows the user to create a stellar account using the acctivation service
• add the corresponding V client call
• update the demo to create the stellar account instead of requiring the user to have a stellar account