Rope2d plugin and Rope (EX9) module

* a generic plugin for creating rope-like vertices and indices for a triangle strip in 2d
* a ex9 module using the plugin to create an ex9 layer

see here for the initial works
http://vvvv.org/forum/something-like-rope-in-dx11

(a dx11 module will be added in the respective gihub repo)