Allow users to change own passwords

Allow users to change their passwords. Right now, the password is directly used for encrypting / decrypting fields and files, if private. It may be better to store a random encryption/decryption-password in the database, which is encrypted with the userpassword. So if the userpassword is changed, the enc-dec-password is decrypted with the old userpassword and decrypted with the new userpassword and no files or other encrypted entries have to be changed and will continue to work.