Fetch the address from Metamask

[matevz]

Put a standard "Connect wallet" button in the top-right corner which connects with Metamask. Then, it fetches the first connected account, pastes its address into TO field and selects the Sapphire ParaTime.

In the future, we could also have another "Connect wallet" with Oasis logo which connects to the wallet extension and does the same thing for consensus layer.

[lubej]

The wallet address could also be sent via a query parameter, as paratime option is. In most demo applications, you already know the address, if you want to navigate to the faucet.

[gw0]

@lubej Your feature request is unrelated to this issue. Can you put it in a separate issue and/or prepare a PR?