[the-overmind] Send some initial XEC with initial tokens

Summary: To support simple on-chain activity across different wallets, users will need XEC. With mature HD wallet methods we could have a more elegant way of supporting this than splitting up XEC across all addresses. But this is a rough and ready method. Given expected activity, and given that users will not be able to withdraw XEC (only tokens), this approach is okay to start with.

Test Plan: npm test

Reviewers: #bitcoin_abc, johnkuney

Reviewed By: #bitcoin_abc, johnkuney

Differential Revision: https://reviews.bitcoinabc.org/D19202