- Refactoring of the mail sending part. Mail queue (table 'queued') is now used also for all test emails.

- More options how to send test emails.
- Fixed problems with pausing a campaign (#593)
- Started rework of transactional sender of templates (#606), however this contains functionality regression at the moment because it does not interpret templates as HBS. It needs HBS option for templates as described in https://github.com/Mailtrain-org/mailtrain/issues/611#issuecomment-502345227

TODO:
- detect sending errors connected to not able to contact the mailer and pause/retry campaing and queued sending - don't mark the recipients as BOUNCED
- add FAILED campaign state and fall into it if sending to campaign consistently fails (i.e. the error with sending is not temporary)
- if the same happends for queued email, delete the message

shared/campaigns.js

@@ -38,11 +38,12 @@ const CampaignStatus = {
 
     // For campaign types: NORMAL, RSS_ENTRY
     SENDING: 7,
+    PAUSING: 8,
 
-    MAX: 8
+    MAX: 9
 };
 
-const campaignOverridables = ['from_name', 'from_email', 'reply_to', 'subject'];
+const campaignOverridables = ['from_name', 'from_email', 'reply_to'];
 
 function getSendConfigurationPermissionRequiredForSend(campaign, sendConfiguration) {
     let allowedOverride = false;