remove plugin value from fixtures

it raises error "Failed opening required 'Plugin/Example/Example.php'" on box site due to defined vagrant configuration constant environment = 'testing'
create admin meterebilling api call cron_generate_invoices

Generate invoices for metered billing orders at first day of a month
create admin meterebilling api call cron_suspend_orders

Suspend orders with metered billing, when invoice is not paid within X days. Default value 15 - days
add metered billing crons to daily boxbilling cron