Optimize logged user check

[2aces]

If there are multiple oca jobs in the queue checking if the user is logged in, admin-ajax will be polled for each one, consumming too many server resources and delaying the queue. We should optimize this.

Considerations:

• Is there any reason for not doing once by page?
• Is a logged_in_status variable with an expiration time a good idea?
• shouldn't check for logged in statys only for jobs with different content for priv users?
• Is it possible to use JWT (JSON Web Tokens)?