Add zoom-in/out animation
Add zoom-in/out animation

Introduce zoom-in/out animation and keep the scaled image there until
the new tiles are loaded. This should prevent the flickering experienced
when zooming and also make libchamplain look more cool.

Distrotech/libchamplain,StanciuMarius/Libchamplain-map-wrapping,Distrotech/libchamplain,PabloCastellano/libchamplain,PabloCastellano/libchamplain,StanciuMarius/Libchamplain-map-wrapping,GNOME/libchamplain,StanciuMarius/Libchamplain-map-wrapping,Distrotech/libchamplain,PabloCastellano/libchamplain,Distrotech/libchamplain,StanciuMarius/Libchamplain-map-wrapping,PabloCastellano/libchamplain,GNOME/libchamplain,StanciuMarius/Libchamplain-map-wrapping,Distrotech/libchamplain,PabloCastellano/libchamplain