Make password field flexible in terms of associated users (mixed/exclusive)

Will review next week

Huh, interesting, that's not in the 8 code base at all, though that should have been in the branch looking at the dates here https://www.drupal.org/node/2033195 Though that's actually in the wrong section in the 7 form, weird.

Anyway, from my perspective adding that checkbox is not an ideal solution since there are essentially three cases which can come up:
- Create a user without LDAP assocation => Needs password
- Create a user with LDAP association (existing LDAP user) => Normally does not require a password though I suppose one could authenticate with Drupal and then sync data over LDAP (ignoring that case for now)
- Create a user with LDAP association (create LDAP user) => Password required

So from my perspective the password field would need to dynamically switch if the radio button is associate and create is deselected. I tried to put that into FormAPI states but something is weird there with the syntax and Google suggests that I'm not the first with problems.

I'd appreciate if someone could help work on this patch or offer feedback if this would require custom JS not supported by states.

Reopening since the conditions on the edit form listed above aren't fully supported yet but disabling the password field in the registration form is added.