[new lokad] Add spec for onchain trollbox for tokens

Summary: See trollbox.md for rationale. Would be a good way for token creators to communicate with their users and vice versa.

Test Plan: proofread

Reviewers: #bitcoin_abc, tobias_ruck

Reviewed By: #bitcoin_abc, tobias_ruck

Subscribers: Fabien, tobias_ruck

Differential Revision: https://reviews.bitcoinabc.org/D17046