First revision of pointer interpretation

Pointers can now look at the element factories below them in the chain
to search for interpretations. If they find one, they display it as
their own. For lists of images/palettes, this can be very useful, as you
can now see the entire list in one place.
Bugfixes for interpretation connect

In the case of pointers, the elements connected to an interpretation may
not all be in a single set: there may be multiple pointers, with space
between, pointing to the same data. The hover connect should check the
index of all elements.

Wrapped elements don't have a grid position: check their parents for a
grid position instead.