Make DateTimeFormatter a service and adjust tests that have been inaccurate

Fix #12227

This change will expose the user backend via the REST API which is a pre-requisite for https://github.com/owncloud/core/issues/12620.

For example:
````json
[{"name":"9707A09E-CA9A-4ABE-A66A-3F632F16C409","displayname":"Document Conversion User Account","groups":[],"subadmin":[],"quota":"default","storageLocation":"\/Users\/lreschke\/Programming\/core\/data\/9707A09E-CA9A-4ABE-A66A-3F632F16C409","lastLogin":0,"backend":"OCA\\user_ldap\\USER_LDAP"},{"name":"ED86733E-745C-4E4D-90CB-278A9737DB3C","displayname":"Hacker","groups":[],"subadmin":[],"quota":"default","storageLocation":"\/Users\/lreschke\/Programming\/core\/data\/ED86733E-745C-4E4D-90CB-278A9737DB3C","lastLogin":0,"backend":"OCA\\user_ldap\\USER_LDAP"},{"name":"71CDF45B-E125-450D-983C-D9192F36EC88","displayname":"admin","groups":[],"subadmin":[],"quota":"default","storageLocation":"\/Users\/lreschke\/Programming\/core\/data\/71CDF45B-E125-450D-983C-D9192F36EC88","lastLogin":0,"backend":"OCA\\user_ldap\\USER_LDAP"},{"name":"admin","displayname":"admin","groups":["admin"],"subadmin":[],"quota":"default","storageLocation":"\/Users\/lreschke\/Programming\/core\/data\/admin","lastLogin":"1418057287","backend":"OC_User_Database"},{"name":"test","displayname":"test","groups":[],"subadmin":[],"quota":"default","storageLocation":"\/Users\/lreschke\/Programming\/core\/data\/test","lastLogin":0,"backend":"OC_User_Database"}]
```

* files_encryption
* files_versions
* files_trashbin
* tests
* status.php
* core
* server container

* this needs to be properly fixed by a proper organisation of the base.php
* introduced fixDIInit() in AllConfig that moves the injection
  of DatabaseConnection to a later point in time
* problems mostly because of the autoconfig setup

* keep old static methods - mapped to new ones and deprecated
* removed deleteApp, getUsers, getApps because they are unused
* make AllConfig unit tests more robust against not cleaned up environments

* introduce SystemConfig to avoid DI circle (used by database connection which is itself needed by AllConfig that itself contains the methods to access the config.php which then would need the database connection - did you get it? ;))
* use DI container and use that method in legacy code paths (for easier refactoring later)
* create and use getSystemConfig instead of query() in DI container

Returns the list of tags that are set on the given object ids.

First step of a somewhat testable user management. - I know, the JSON returns are in an ugly format but the JS expects it that way. So let's keep it that way until we have time to fix the JS in the future.

This is a first draft. It has only been tested with the ownlcloud logger.
Some internal fields are JSON encoded several times which makes it harder to read.

Most of the normalizer is borrowed from Monolog
https://github.com/Seldaek/monolog/blob/master/src/Monolog/Formatter/NormalizerFormatter.php

The codepath that is executed when executing ownCloud via CLI is different than via browser. Specifically, the config is created by the user session already in `OC_Util::getInstanceId()` by a call to `setValue`. That said, this seems to be quite a bad side-effect, but for the sake of "not breaking whatever might break if we touch this" let's keep it that way for now.

When executing the autoconfig via `php -f index.php` the said session was not setup and thus no `config/config.php` file was created resulting in an installation error.

To reproduce this try to setup ownCloud via `php -f index.php` with and without that patch. (ensure to delete all existing configs before and don't access ownCloud with a browser in the meantime)

Fixes itself.

Both are removed from 5.4.0

Safe Mode: http://php.net/manual/en/features.safe-mode.php
> This feature has been DEPRECATED as of PHP 5.3.0 and REMOVED as of PHP 5.4.0.

Magic Quotes: http://php.net/manual/en/security.magicquotes.php
> This feature has been DEPRECATED as of PHP 5.3.0 and REMOVED as of PHP 5.4.0.

Otherwise the headers from `JSONResponse` are gone and the Content-Type of the response would be `text/html` instead of `application/json; charset=utf-8`. This leads to broken scripts since we set the `nosniff` tag, furthermore this is very bad from a security PoV.