oram

Switched the ORAM initialization approach from explicit to lazy. Motivation: The existing explicit initialization had a security flaw, found by Hao Chen. While this flaw could be easily patched, I thought it would be better to drop explicit initialization entirely in favor of lazy initialization, which is standard in the Path ORAM literature. Details: Before, the ORAM was explicitly "zero-initialized" **. More precisely, initialization guaranteed that for all addresses `` is found, the ORAM returns zero. Technically, "initialized to a default value".