Follow-up bc1f601382, which added a group to load.php, but I forgot
to add api.php to its group.
Also, fix the pre-existing group that thumb.php and thumb_handler.php
were a part of. It looks like the entire "Media" group was not
defined anywhere, so it was ignored by Doxygen. This is now fixed.
Change-Id: Iba487aac5883f66b81f2496a38a3c978d5e6600b
7639aa869a