Add relayer that can simulate a big trie

[s1na]

The current token relayer generates random keypairs, creates accounts under the address derived from the pubkey and inserts them into the trie, and later on uses the private key to sign txes.

Because keypair generation is computationally intensive and how we handle memory is not optimal, simulating a large trie (e.g. mainnet height) is not feasible.

We could alternatively generate a lot of "dumb accounts" (empty with no keypairs) and then add a few "full accounts" to sign txes with later on.