Provide default constructors and move constructors to source (*.cpp) files.

[Quaker762]

Because some OGL objects need a context before they are initialised, I think it's best if we provide a default constructor so functions such as Load( ) (for example, a shader program) can be called later instead of being automatically called by the constructor.

This also makes a bit more sense, as the we can specify something like

sh3::gl::program test;test.Load("program");

instead of having to specify the program name when the object is declared, so we can defer the loading to when we actually need it (like loading an msbmp later, not during object construction).

This will mainly affect sh3::gl::program, sh3::graphics::texture, sh3::graphics::msbmp etc.