This reverts commit 6a1a4880.

`server` is completely wrong here and this will not work on master. With `getParam` it will work fine though.

Testplan:
- [ ] Without patch: Share a file and try to access `http://localhost/public.php?service=files&t=THESHAREDTOKEN` => Fails
- [ ] With patch: Try the same => Works

Master only.

This changeset removes the static class `OC_Request` and moves the functions either into `IRequest` which is accessible via `\OC::$server::->getRequest()` or into a separated `TrustedDomainHelper` class for some helper methods which should not be publicly exposed.

This changes only internal methods and nothing on the public API. Some public functions in `util.php` have been deprecated though in favour of the new non-static functions.

Unfortunately some part of this code uses things like `__DIR__` and thus is not completely unit-testable. Where tests where possible they ahve been added though.

Fixes https://github.com/owncloud/core/issues/13976 which was requested in https://github.com/owncloud/core/pull/13973#issuecomment-73492969

To prevent unexpected behavior, public.php and the OCS API calls will
return 503 Service Unavailable when an upgrade is due.

The getfile routing code was absolutely legacy and not needed anymore. Additionally \OC::$REQUESTEDAPP was never set to the actually accessed application.

This commit removes the legacy routing code and ensures that $REQUESTEDAPP is always set so that other applications (e.g. the firewall or a two-factor authentication) can intercept the currently accessed app.

Testplan:
[x] Installation works
[x] Login with DB works
[x] Logout works
[x] Login with alternate backend works (tested with user_webdavauth)
[x] Other apps are accessible
[x] Redirect on login works (e.g. index.php?redirect_url=%2Fcore%2Findex.php%2Fsettings%2Fapps%3Finstalled)
[x] Personal settings are accessible
[x] Admin settings are accessible
[x] Sharing files works
[x] DAV works
[x] OC::$REQUESTEDAPP contains the requested application and can be intercepted by other applications

This can be enabled by setting 'singleuser' to true in config.php

set incognito mode for public.php calls. Because in this case ownCloud should always work the same way as if no user is logged in

This is for all LowerCaseConstant warnings

respect coding style