Add support for password hints

[therden]

Thank you for making and sharing this plug-in.

Please consider adding support for optional password hints that are saved at encryption time and then presented to the user when encrypted text is selected for decryption.

By reducing the risk of being unable to recall the password required to decrypt a block of text, password hints would encourage users to employ as many different encryption passwords as make sense in their use-case.

[meld-cp]

That's a good idea 👍

[therden]

Password hints work great -- thank you for implementing them!