Improvements to the Users module and several minor fixes

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | --
| Fixed tickets | #991, #973
| Referenced tickets | #900
| License       | MIT
| Doc PR        | zikula/zikula-docs#123

| Author | commit title | commit | description
| ---------- | --- | --- | ----
cmfcmf | refs 89997c6 |	9250033 |  Closes #991
cmfcmf |	Fixed some E_NOTICE's. |	408d0f7 | Refactoring to new module names
cmfcmf |	Fixed to match the latest changes. |	0496757 | Updating robots.txt
cmfcmf |	Fixed E_Notice |	b77246c | Correct array handling
cmfcmf |	Better hook error messages |	225fdea | Do not just display an empty page if no subscriber are available
cmfcmf |	Fixed fatal error. |	dd33f34 | Missing date format caused it.
cmfcmf |	Made third party auth modules working, closes #973. |	f812647 | :-)
cmfcmf |	Do not say 'Login with your password', if the user has no password set; Do not display 'passreminder', if the user has no passreminder set, refs #900. | 902c094 | Improvements for third party auth modules