Warning when cron task is not running

[Hipska]

It would be very handy to have an informational message at the top of the page indicating the cron.php is (possibly) not running.

This could be detected when all active background tasks have a next run date in the past.

A similar notice could be placed on the Async tasks page mentioning the ExecAsyncTask is paused.

[Molkobain]

Hello @Hipska , thanks for the idea, it sounds like a good improvment indeed!
I'm not sure I could implement this soon, but feel free to make a PR :)