a struct Texture to store a sf::Texture and the application's texture sizes,
- add a texture resources manager and retrieve codes to allow - if needed,
rescaling startsplash and spidlogo at startup - loading some graphics with
different resolutions: buttons, inventory, pcedbuttons, statarea,
startanim, startbut, startup, terscreen, textbar, transcript can be
used to load high resolution pictures.
Note: currently, render_image and res_image are a mess as Texture and sf:Texture classes
cohabit :-~
