split mail and mailserver

mail = all the per-domain code
mailserver = all the mail server level code

src/taskworker.js

@@ -12,7 +12,7 @@ const apptask = require('./apptask.js'),
     dyndns = require('./dyndns.js'),
     externalLdap = require('./externalldap.js'),
     fs = require('fs'),
-    mail = require('./mail.js'),
+    mailServer = require('./mailserver.js'),
     reverseProxy = require('./reverseproxy.js'),
     safe = require('safetydance'),
     settings = require('./settings.js'),
@@ -28,7 +28,7 @@ const TASKS = { // indexed by task type
     setupDnsAndCert: cloudron.setupDnsAndCert,
     cleanBackups: backupCleaner.run,
     syncExternalLdap: externalLdap.sync,
-    changeMailLocation: mail.changeLocation,
+    changeMailLocation: mailServer.changeLocation,
     syncDnsRecords: dns.syncDnsRecords,
     syncDyndns: dyndns.sync,
     updateDiskUsage: system.updateDiskUsage,