fix shader reload, maintaining the shared shaders in the World #87

- creating only one glow::Shader instance per shared shader file
- the World is now is a singleton (seems reasonable), so that it's easier accessed from classes the need the lighting/ shared shaders
adopt cgsee's phong lighting to fit better with elemate's needs #87

- sunlight without direction
- phongLighting glsl function only takes parameters for current position/normal/material and secondary light source
some more shared shaders #87
fix #87, early bailing in shadow mapping

- wrong output values for fully in the shadow/light
- add early bail sample in the center of the testing area
fix typo. #87
Merge pull request #88 from lanice/shadingIssues_87

Shading issues 87