jsDump: Add a depth parameter to object parsing

In projects with deep object graphs, like Ember, walking all properties
of an an object recursively can end up walking most of memory. This
causes the browser to run out of memory and kill the tab/thread.

This introduces a depth option for the parse function, which is used in
places where an strictly accurage output of an object is not needed, for
instance, when showing two un-equal object in test output.