Vertices Sort

A mesh aware vertices sorting node use the stable python sort.
Mesh with unclear order of order after remove doubles.
![unsorted-mesh](https://cloud.githubusercontent.com/assets/6241382/2756596/4656942e-c979-11e3-9f6d-df39b4187808.png)
Sort XYZ. Should be able to define sorting order, for example Y X Z.
![sortxyz](https://cloud.githubusercontent.com/assets/6241382/2756597/4656a05e-c979-11e3-975c-d5a0fcd783a7.png)
Distance from a point
![sort-dist](https://cloud.githubusercontent.com/assets/6241382/2756598/4656f4be-c979-11e3-9424-c0666bc43fbc.png)
The user creates the sorting criteria. In this case the Y values.
![user-sort](https://cloud.githubusercontent.com/assets/6241382/2756595/46565d92-c979-11e3-8810-b5cd39f549a1.png)