Add cron.php

Is your feature request related to a problem? Please describe

On some mutualized hosting you can't add any parameter to cron tasks.

Describe the solution you'd like

Therefore we need a cron script that doesn't require any parameter, such as this public/cron.php:

<?php
print "Castopod Cron - Starting...\n";
print 'PHP_BINARY: '.PHP_BINARY."\n";
exec(PHP_BINARY.' index.php scheduled-activities');
exec(PHP_BINARY.' index.php scheduled-websub-publish');
exec(PHP_BINARY.' index.php scheduled-video-clips');
print "Castopod Cron - Done.\n";
?>

Describe alternatives you've considered

Create a php only script (without any exec)

Additional context