Forgot password made nicer

Fixes #5886

Tested manually:
* forgot password
* change password from user settings
* reset password from admin

To do:
 * [x] change chore to feature in first commit
 * [x] add more details to feature commit
 * [x] send reset message when not password parameter set in `execute_new_password_request()`
 * [x] use `force_user_password_reset` function in admin/user/resetpassword action