SpotLight per vertex lightning

Here is an implementation for **SpotLight** in the default shader and with an example.

According to the OpenGl standart, this light includes the attentuation (constant, linear, quadratic) and the cutoff and exponent.
Because shader are currently on per-pixel lightning, the cutoff can be not so nice, *but a per-fragment lightning is being studied*. I'm not at all a shader master, so any recommendation, suggestion, change or whatever would be appreciated.
I'm also here to answer any questions if you have some.