Add helper function to generate unsubscribe links

This is so that we can bulk-generate them to add to places like
ChipChoc.

generate-unsubscribe-links.js

@@ -0,0 +1,61 @@
+let {
+  Pledge,
+  makeSerialiser,
+} = require('./server')
+
+function generateBackoutLink(email, unsubscribe=true) {
+  let serialiser = makeSerialiser(email)
+
+  // format "unsubscribe" for serialisation
+  let staySubscribed
+  if (unsubscribe) {
+    staySubscribed = 'no'
+  } else {
+    staySubscribed = 'yes'
+  }
+
+  let verificationLink = `https://fund.snipettemag.com/back-out?email=${encodeURIComponent(email)}&key=${encodeURIComponent(serialiser.dumps(staySubscribed))}`
+
+  return verificationLink
+}
+
+async function generateBackoutLinks(unsubscribe=true) {
+
+  // get list of pledges
+  let pledges = (
+    await Pledge
+    .forge()
+    .orderBy('created_at', 'DESC')
+    .fetchAll()
+  ).models
+
+  let verificationLinks = []
+
+  // get the links
+  pledges.forEach((pledge) => {
+    verificationLinks.push(
+      generateBackoutLink(pledge.get('email'), unsubscribe)
+    )
+  })
+
+  return verificationLinks
+}
+
+if (!module.parent) {
+    // figure out if we should unsubscribe
+    let unsubscribe
+
+    if (process.argv[2] == 'yes' || process.argv[2] == 'stay-subscribed') {
+      console.log('Backing out but staying subscribed')
+      unsubscribe = false
+    } else {
+      console.log('Backing out and unsubscribing')
+      unsubscribe = true
+    }
+
+    // get the links and print 'em out
+    generateBackoutLinks(unsubscribe).then((links) => {
+      links.forEach(link => console.log(link))
+      return
+    })
+}