Add "Edit Caption" to embedded gallery for logged-in users

Pops up the filemanager Properties window from a layout.  Requires `$page->add_script ('/apps/filemanager/js/jquery.filemanager.js');` in the handler and `{! filemanager/gallery?path=path/to/images&amp;style=embedded !}` in the layout.

![screenshot-2013-04-05-14:19:59](https://f.cloud.github.com/assets/3870415/345273/9b02eee2-9e1d-11e2-9a12-79214567b3a7.jpg)

![screenshot-2013-04-05-15:21:31](https://f.cloud.github.com/assets/3870415/345574/12209a62-9e26-11e2-8def-06869a2cf5ad.jpg)