Add functions, loaded in OngooServiceProvider

This is done, to add overiding.
functions are:
 \now() which is an alias to $app['now']() which return a new
\DateTime()
 \datetime() which is an alias to $app['to_datetime']($datetime) which
transform a string|DateTime to a \DateTime
 \deciaml which is an alias to \round($number, 2, PHP_ROUND_HALF_UP)
 \trans(…) which is an alias to $app['translator']->trans(...)
 \transChoice(…) which is an alias to $app['translator']->transChoice(…)