Was: Clean up for "LzUtils" or nullify more attributes after destroying a view.

Callbacks made through the "LzUtils.callback"-mechanism lead to possible memory-leaks, as there is no clean-up and therefore you can easily resurrect i.e. <img> from memory (as shown in the attached testcase).

Two proposals:
1. nullify more attributes after destroying a view (and sprite) to delete memory-consuming references
2. install a "clean-up"-mechanism for "LzUtils.callback"