Added button to hide passphrase so they are not displayed as plaintext. The private key will still be displayed though.
Added PBKDF2 support (right now using 100000 iterations) for more secure hashing. This gives some extra safety for lower entropy passwords, and since it's unlikely for this page to be used too often we want to use as high number of iterations as possible (maybe higher?)

Originally used CryptoJS but their PBKDF2 implementation was too slow so switched to using Stanford's more efficient sjcl library. Still need to download and cache the code.
Cleaned up CryptoJS commented out code.