Schedule

[ItHasU]

Allow the schedule of MQTT messages to postpone the publishing of a payload on a topic.

[ItHasU]

We should be able to set time :

• [x] as UTC timestamp,
• [x] as now + duration&unit.

[ItHasU]

• [x] Scheduled messages should be saved on exit.
• [x] User should be able to cancel a scheduled message (from UI & API)
• [ ] Messages should have an expiration date in case server is stopped then reloaded

[ItHasU]

• [ ] Allow to override previously set topic, or clear scheduled messages
• [ ] View scheduled messages and allow to cancel from ui