I updated Ubuntu Gnome, Gnome version to 3.12 and was trying to figure out how to make categories within the application menu. I tried using the dconf-editor (org > gnome > shell : app-folder-categories) method, but the option isn't available in 3.12. The only way I've found that would allow you to make categories is through Gnome Software and so far I haven't been able to find a way of downloading it.
Just type in a terminal:
sudo apt install gnome-software
You can download Gnome Software here. Once downloaded expand the file, and look in the INSTALL file for information on how to install. You have to build the file from source, or you can take a look at this. Basically the steps to follow are:
./configure make make install