WIP: make it possible for users to sign activities

migrations/2018-05-03-163427_user_add_keys/down.sql

@@ -0,0 +1,3 @@
+-- This file should undo anything in `up.sql`
+ALTER TABLE users DROP COLUMN private_key;
+ALTER TABLE users DROP COLUMN public_key;

migrations/2018-05-03-163427_user_add_keys/up.sql

@@ -0,0 +1,3 @@
+-- Your SQL goes here
+ALTER TABLE users ADD COLUMN private_key TEXT;
+ALTER TABLE users ADD COLUMN public_key TEXT NOT NULL DEFAULT '';