Add script to compose translated Journal index images

At the moment this only displays one line and cuts the text off -
wrapping the text AND centering it vertically is a bit of a problem.

I can set a fixed width to wrap the text easy enough, but I can only
guess as to what the height should be - too small and it cuts off, too
large and I won't be able to center it vertically.

Not sure what to do about this - maybe a patch to the GIMP to allow the
text box size to be set to fixed width & dynamic height? Or a patch to
explicitly support vertical centering? Or just hack together a word
wrapping algorithm in these scripts and leave the size as dynamic?
Implement my own word wrapping function for journal index images

See the previous commit message for the problem description. This seemed
to be the easiest solution to implement in a hurry.