Add blacklist functionality

migrations/1556582597515-blacklist.js

@@ -0,0 +1,17 @@
+var db = require('./db')
+
+exports.up = function (next) {
+  const sql =
+    [`create table blacklist (
+        crypto_code text not null,
+        address text not null,
+        unique (crypto_code, address)
+      )`
+    ]
+
+  db.multi(sql, next)
+}
+
+exports.down = function (next) {
+  next()
+}