Add method getSeasonalGalleries

There is a problem with arg theme_id : cannot to be set to 0 (zero) for
get all galleries. So script will added it to args if the $theme_id is
more than 0
rewrite method getSeasonalGalleries in PHP Kit

rewrite $args array
$theme_id set default to null
Merge pull request #7 from defro/master

Add method getSeasonalGalleries