Add the ability for users to change the wallet password

[aaroncox]

Currently there is no way to change the local wallet password. This should be added and tested very well before releasing.

It will need to:

• Request the current password.
• Request the new password (then prompt to confirm).
• Decrypt the local keystore with the current password.
• Encrypt the decrypted data with the new password.
• Re-save the new encrypted keystore to local storage.
• Remove and recreate the wallet hash.

[jorfermo]

Any progress on this ?

[aaroncox]

No - but I think a few other parts of Anchor have improved enough that we could revisit it soon. I'll mark the issue for our next milestone and see if we can implement it more easily.