Notebook pages will be sorted in order by layers

It is very difficult to tell what layer number you have moved a feature to. Instead of adding another control to compensate for this, we can just sort the notebook pages into the same order as the layers. I've gotten this to work in a quick Ruby demo. This will be a little different here, because there are a lot of pieces of code that are dependent of those pages being in the same order. I also want to make a bonus change to the file structure to make it easier to maintain.

The new file structure will be like this:
==Feature
====Head
======round_square_jaw.svg
======square_fat_neck.svg
======loading.png
======label.png

All the things that will be changed:
1. Feature sets will be loaded based on their file structure
2. The loading page will use the feature/blah/loading.png image for each feaure
3. The notebook pages will use the feature/blah/label.png image for each label
4. The notebook pages will be sorted based on the layer ordering of the features in the avatar
5. The first layer will be on top, and last layer on bottom. Pages that have no layer selected will be at the bottom.
6. The default 'weight' of each feature layer will have to be stored in a config file or a Python array
7. Once done, the Glade file and code will no longer be dependent on preexisting feature categories.
8. Artists will be able to just drop their features in the correct folder, or create a new folder for new features.

Once this is done, it will be easier to give each feature its own name as in this spec:
https://blueprints.launchpad.net/memaker/+spec/name-all-objects