Add keyboard shortcuts
Add keyboard shortcuts

This commit add many future API additions for libchamplain

Arrows: move around by 1/4 of the viewport size's
Ctrl+up/down: zoom in, zoom out of 1 level

The scrolling will be smooth if in KINETIC mode, otherwize
non smooth (as center_on would do).

GNOME/perl-Gtk2-Champlain,Distrotech/libchamplain,StanciuMarius/Libchamplain-map-wrapping,StanciuMarius/Libchamplain-map-wrapping,potyl/champlain,PabloCastellano/libchamplain,GNOME/libchamplain,Distrotech/libchamplain,Distrotech/libchamplain,potyl/champlain,potyl/champlain,GNOME/perl-Gtk2-Champlain,Distrotech/libchamplain,PabloCastellano/libchamplain,GNOME/libchamplain,StanciuMarius/Libchamplain-map-wrapping,GNOME/perl-Champlain,Distrotech/libchamplain,StanciuMarius/Libchamplain-map-wrapping,PabloCastellano/libchamplain,potyl/champlain,GNOME/perl-Champlain,StanciuMarius/Libchamplain-map-wrapping,PabloCastellano/libchamplain,PabloCastellano/libchamplain