New menu item: add user

Today I added a new menu item where users can add new users. An activation email will then be send to them.

GSoC coming to its end

August 20th at 19:00 UTC is pencils down time. This means I will be evaluated based on the code produced until that time. JCpg isn't fully completed at the moment so more work is required. And of course, I will continue working on it after the SoC ends. I just did a complete code structure and comments check and am now in the process of taking a backup because the current code's state must be sent to Google in the following weeks.

Extending synchronization

At this point I'm finetuning the synchronization process:

First all the not yet uploaded components are sent to the server
Then, all the components on the server not yet saved locally are downloaded

Introducing scrollbars

The explorer and edit windows now use scrollbars so it's also possible to work with large pictures.

Major picture cellrenderer bug fixed .. finally

After searching for this for quite some time, I finally managed to solve this bug. Before the fix, pictures were repeated and weren't always clickable and this all caused nothing but problems. Now it's fixed and each picture has a nice border now.

Infinite subcategories and subalbums

Categories can now have an infinite number of subcategories and the same counts for all these subcategories and so on. All this information is now correctly saved and loaded when necesarry.