Add password manager support

[zeroby0]

Elements in the Signup and Login pages don't have sufficient labels and attributes for password managers to identify them and offer to auto-fill. This PR should enable most password manages to identify them and also slightly improve accessibility.

The passwordrules field is to help password generators, and will not get in the way of users using whichever password they choose to.

Made with the help of:

• https://developer.apple.com/password-rules/
• https://hidde.blog/making-password-managers-play-ball-with-your-login-form/
• https://developer.1password.com/docs/web/compatible-website-design/
• https://support.lastpass.com/help/how-do-i-configure-my-website-to-work-with-lastpass

The autocomplete field values are updated to match that of lichess.com, which also happen to be best practices and are useful for password managers.