Add initializer list variants for setData(...)

This is required as set_data otherwise does not accept initializer_lists of specific types.

Before the following would not work:

my_texture.setData<uint8_t>(GL_R8, 4, 2, {1, 2, 3, 4, 5, 6, 7, 8});

as the implementation

template<class DataRangeT> 
void setData(GLenum internalFormat, int width, int height, DataRangeT&& data, int mipLevel){}

does not match correctly.

assigned to @ptrettner

mentioned in commit eaeef008

merged