Feature/delayed and scheduling messages

[rhyslbw]

Previously discussed here: meteor-space/event-sourcing#4

vsivsi:job-collection has built in support for later.js

[darko-mijic]

There are many ways to implement the APIs for this. 3 ideas came from the discussion on Slack.

1. new signature for commandBus.send(), something like this:
   commandBus.send(command, {later: aLaterJsObj } )
2. new method for delayed sending of commands:
   commandBus.sendLater(...)
3. specialized Command class:
   Space.domain.Command extended with more specialized Space.domain.DelayedCommand which could have a constructor that accepts all data needed for delayed sending. That data can be saved in metadata of the command and the signature of commandBus.send() method would not change and it could be used for sending all types of command.

[rhyslbw]

We could even retain the same Command class and just have an optional meta.later properly. The Command isn't really characterised by the fact that it's delayed, but carrying the metadata seems reasonable