#38 Images instead of string values

[Roel Hertoghs]

Usage of images as values for cells, mapped via some
allowed values keys.

E.g. for chinese symbols, egyptian symbols, national
flags, female celibrities (non-nude please), ...

The panel may have to grow somehow, in size.
Technically, height and width of the table model will
have to align with the images height & width.

It has to be checked how such a "value" can be
inserted, maybe via some new button set, with the
images showing.

If allowed values progress (see feature request
1492382) can still be shown, has to be checked, too.

Image sets maybe via optional packs at izPack install
time, to avoid longer installment package? Possibly
later (out-of scope for this feature) via the kagiru
website.