admin: Add etherpad update check

This update check notifies admin on startup (via console) or in /admin UI that they need to update Etherpad.

src/node/utils/UpdateCheck.js

@@ -0,0 +1,44 @@
+const semver = require('semver');
+const settings = require('./Settings');
+const request = require('request');
+
+let infos;
+
+function loadEtherpadInformations() {
+  return new Promise(function(resolve, reject) {
+    request('https://static.etherpad.org/info.json', function (er, response, body) {
+      if (er) return reject(er);
+
+      try {
+        infos = JSON.parse(body);
+        return resolve(infos);
+      } catch (err) {
+        return reject(err);
+      }
+    });
+  })
+}
+
+exports.getLatestVersion = function() {
+  exports.needsUpdate();
+  return infos.latestVersion;
+}
+
+exports.needsUpdate = function(cb) {
+  loadEtherpadInformations().then(function(info) {
+    if (semver.gt(info.latestVersion, settings.getEpVersion())) {
+      if (cb) return cb(true);
+    }
+  }).catch(function (err) {
+    console.error('Can not perform Etherpad update check: ' + err)
+    if (cb) return cb(false);
+  })
+}
+
+exports.check = function() {
+  exports.needsUpdate(function (needsUpdate) {
+    if (needsUpdate) {
+      console.warn('Update available: Download the actual version ' + infos.latestVersion)
+    }
+  })
+}