Allow calling hooks multiple times in same file

[jeremyboggs]

You currently cannot use add_plugin_hook() for the same hook multiple times in the same file. E.g.:

add_plugin_hook('public_theme_header', 'function_one');
add_plugin_hook('public_theme_header', 'function_two');

Omeka only seems to apply the last one, if the hook is called multiple times in the same context.

This wouldn't be such a big deal, except that its currently not possible to actually hook into the public_theme_header from your theme's custom.php file because that hook is already getting used in application/views/scripts/custom.php.

(It also appears that custom header backgrounds aren't getting added either, because of the addition of the admin bar in 1f98075253d7eb7627499f3ec46b45cd2336ef01.)

It would be very nice to be able to use the public_theme_header hook in your theme's custom.php, so you could do things like queue your css and javascript assets in there, and add them with the hook, instead of adding them directly to the common/header.php template file.

But more broadly, it would seem beneficial to allow calling the same hook multiple times, given all the ways that things are loaded in Omeka.

[jimsafley]

Would something like this work?