closes#5489
- Remove unneeded Promise.promisify in mailer
- Remove noEmailTransportConfigured error as not relevant anymore (Direct is default)
- Clone message argument in mailer.send
- Move test from api_mail_spec to mail_spec
- Add default mail title test
* ref #5345 and #3801
* creating helper methods for dealing with i18n initialization, polyfill and string+compilation
* initial structure for server-side JSON language file