See #4716

- Added missing return statement
- Added missing support for SEEK_END
- Fixes #5524

- remove property only if present

The logo images are specified in the php templates with eg `image_path('', 'logo-wide.svg')`. If that file exists the correct path will be served to the client in the html template. Then the `SVGSupport()` is checked in https://github.com/owncloud/core/blob/master/core/js/js.js#L701 which will replace `svg` with `png` in img tags and css background definitions.

fixes #5074
partially solves #5421, but not when an svg has been specified in css and is then 'fixed' by js to point to a png which does not exist in the theme but is then might be resolved to an image from core .... well theoretical problem ... might not even be a problem

@karlitschek @jancborchardt please review

When two scanning processed run at the same time, for example when
scan.php and list.php were called at the same time on an external
storage mountpoint, duplicate insertion errors can occurs.

These errors are now logged and ignored.

Since both scans are running in parallel transactions, they don't see
each other's changes directly in the DB which can cause duplicate
insertion errors for mime types as well, but those mime types can't be
selected yet. The solution to this is to force-reload the mimetypes list
after the transaction is finished.

Fixes #5199

To avoid having to use OCP\Appframework\Http\Http in the public - and stable
- API OCP\Appframework\Http is now both a class and a namespace.

- move properties on node move

Undefined variable: this
lib/private/appframework/dependencyinjection/dicontainer.php:92

 /ocs/cloud/user
Response:
 <?xml version="1.0"?>
 <ocs>
  <meta>
   <status>ok</status>
   <statuscode>100</statuscode>
   <message/>
  </meta>
  <data>
   <id>thomas</id>
   <display-name>DeepDiver</display-name>
   <email>no-response@domain.tld</email>
  </data>
 </ocs>

add options to disable the check for a working .htaccess file in data and for a working WebDAV server. This are advanced settings that are needed in special situations where our check fail and the user runs into an http timeout.

removing pointless calls on quoteIdentifier() - reason: name on $tableDiff doesn't exist and my design the name cannot be changed
adding PHPDoc