Remove the automatic check for data migration from every request, removing it from the `init` hook.

[andergmartins]

In the file publishpress.php we have a hook to the init action, that calls the method action_ini_for_admin.

This method will run a check for the current version, and call the upgrade method for each module.

This kind of task should run async, displaying an admin notice asking to the admin to run it.

But what happens if the admin miss the notice, until he enters the admin?

[andergmartins]

This can maybe help on the issues #578 and #808