Add cron scheduler component

[sarnowski]

Add a cron scheduler component with which you can scheduler functions, leveraging dependency injection similar to the http component.

Hint: integrate with #2 in order to allow :local or :global locking of jobs

[sarnowski]

basic cron component implemented but no cluster functionality yet

[lasomethingsomething]

Hey @dryewo, is this suggestion still in scope? If so, let's add a Help Wanted label. If not, let's close.