Faucet transfers from extension

[jurevans]

Opening this issue to discuss how we might bring back faucet transfers the interface (or now, extension), as that would simplify testing for users when connected to a devnet.

We originally had a check in the interface when running yarn dev:local that would automatically fund accounts with 1000 tokens (NAM/ETH/BTC/etc). It might be better to simply have an additional UI button and Amount form available when connected to a devnet. As transactions are executed in the extension, it would make sense that they are initiated there, and could dispatch an event to update balances in the interface (if it is currently connected).

Also, as we need to add balances to the Extension accounts overview, it would be more clear that an account has been funded if it was immediately apparent in the extension itself.

NOTE We could just use the presence of a env variable for faucet address to determine if we display a fund via faucet form to users - would be the simplest approach.