Memory layout visualization feature

[derekbruening]

This is a feature request for visualizing the objects on the heap, pointers between them, and pointers between the heap and stack. The target is small intro-CS-course programs where there are not many objects. The idea is to start by doing something akin to a leak scan but only over heap objects allocated after the entry to main() (so we require symbols) and over thread stacks, but stopping for the primary thread when the main() frame is passed. Scaling to large programs is not an up-front goal.

[johnfxgalea]

This is actually a pretty interesting and useful feature!