added lodepng to the backend CMakeLists.txt
lodepng.{h,cpp} added
added gl_Texture.cpp to opengl/CMakeLists.txt
Propper error handling in gl_Program.cpp
Added opengl/gl_Texture class
Updated test code (multi texturing test)
test shader and material: multi texturing test.
IMaterial: Changed naming of uniform setters (+ added const uniform setters)
Added BaseException class in lib/Exception.h
Updated Uniform.h and Material class to add support for new uniform setters

The Material class loads textures now. (In dev)
Added all the semantics binding to the gl_Program class

The MeshLoader sets the numberOfVertices form the input file
Fixed attribute calculation in Model class
Added support for texture binding and varying vertex count in Renderer class