Add shader_program component

[fayalalebrun]

I've created the class files for the shader_program component. This component will take a vector of shaders and be in charge of linking them, as well as provide methods to pass variables to the encapsulated OpenGL shader program.

[fayalalebrun]

I've defined the general methods and variables needed to link and compile the Shader Program in the header file.

[fayalalebrun]

I've implemented all of the functions related to the creation and compilation of shader programs. I based this implementation on the implementation for the shader stages.