add stealth_address class.
add stealth.hpp to wallet.hpp
install wallet/stealth.hpp header
stealth stubs
temporary ec math abstracted API. once we migrate to non-openssl code, I suspect the API will change/improve.
Revert "temporary ec math abstracted API. once we migrate to non-openssl code, I suspect the API will change/improve."

This reverts commit 21204fb3ca1b5d6c6a2f7bb0523af02ffb36916e.
Port hd_keys to the new ec_keys
Switch key_formats to the new ec_keys system
Use to_data_chunk in key_formats