demos: zip_container: Use clipped blit.

Otherwise the example fails on assert() in GP_Blit.c when image is
larger than screen window.

Signed-off-by: Cyril Hrubis <metan@ucw.cz>
loaders: PSP: Add some more metadata.

Signed-off-by: Cyril Hrubis <metan@ucw.cz>
loaders: Loader: Implement GP_LoaderReadImageEx()

* Implement GP_LoaderReadImageEx

* Add missing ReadImageEx for BMP, PSD and PSP

Signed-off-by: Cyril Hrubis <metan@ucw.cz>