The behavior of Crypto::UnsignedBigInt::export_data unexpectedly
does not actually remove leading zero bytes when the corresponding
parameter is passed. The caller must manually adjust for the location
of the zero bytes.
This patch implements and tests window.crypto.sublte.generateKey with
an RSA-OAEP algorithm. In order for the types to be happy, the
KeyAlgorithms objects are moved to their own .h/.cpp pair, and the new
KeyAlgorithms for RSA are added there.
