Piwigo support for Shotwell

Finally done, uploading event comments from Shotwell to Piwigo.

My favorite photo editor and management program is Shotwell, written for the GNOME desktop but usable under any desktop environment.

For my web gallery I use Piwigo, a very powerful but still easy to handle web photo album.

Over the last year I have contributed quite some code to Shotwell code base, mostly improvements of the piwigo connector (sub-albums support, use title as comment, suppressing of tag upload, and later on support for adding comments to photos, videos, and events (media comment, event comment).

Recently I am working on supporting and linking comments from Shotwell to Piwigo (upload photo comments), and just the other day I have also implemented the ability to upload event comments to piwigo, which finally allows me to keep all information local, the description of each photo, of the whole event, and use Shotwell to upload to Piwigo (and Facebook, if necessary).

The last change is unfortunately still not now (2013-02-26) in the main shotwell development tree, but I am happy that my local build works nicely and uploads to Piwigo have become much more convenient.

On a side remark, Shotwell is written in Vala, somehow similar to C#. All the code written was actually my first code ever in Vala, and mostly done by looking at other code from the project. I think the most complicated part is to understand to object hierarchy of Shotwell, and unfortunately there is no graphical object and method browser for exploring it. But no, I will not be the one who writes it.