Arrows/Spacebar navigation and minor fix

[victor]

Hi all,

minishowcase goes to v09b136, adding minor cosmetic fixes for some
ugly lines in the menu items, and a nice yet underdeveloped and
undocumented hack: <strong>now you can navigate the images by clicking
the left and right arrows! To go forward you can also use the
Spacebar</strong>.

The navigation behaves identical as the image arrows, so when it
arrives to the end of a thumbnail block it automatically loads the
next one.

Hope you like it. There are minor things I still have to check, and my
most important milestone is the creation of subgalleries and updating
the documentation.

Thanks again for all your support, without which all this improvements
would just not be possible.