Allow for manual customisation when generating password.

[bas-d]

We currently generate a password with either default values or, if a PPD exists, with the PPD values. We should allow a user to customise the settings to generate a valid password. If a PPD exists, we could pre-fill the password generation settings sheet with the values from the PPD. This applies to:

• Creating a new account manually in the app
• Creating a new account with the chiffCredentialProvider.
• Updating an account manually in the app

[bas-d]

Also refactor use same code as AddAccountViewController in the chiffCredentialProvider