Include profileicon in $supportedartefacttypes

[kenneth-hendricks]

I dont think there is any reason to exclude profileicons from being stored externally.

1. Verify that there is no reason to exclude profileicons
2. Add 'profileicon' to the $supportedartefacttypes array: https://github.com/catalyst/mahara-module_objectfs/blob/master/classes/object_manipulator/manipulator.php#L50