Added support for extra backends

Somebody had forgotten "OC_User::setupBackends();"...
Added ownCloud backend for external storage

To make it possible to use the short ownCloud URL (without specifying
webdav.php or remote.php), a new backend is available for ownCloud.

The user must specify the host + context path in the "Url" field (which
is mapped to the "host" parameter) and the subdir to mount in the "Root"
field.

This is to prevent confusion because some users forget to append
webdav.php or remote.php to the WebDAV URL.

Fixes #4923
No decimal points for Kilobyte and Byte #5371.
Symfonys addCollection() with multiple arguments is deprecated, fix deprecation warning
correctly mark app management active
Moved content disposition code+workarounds to OCP\Response

Added new OC\Response API called setContentDispositionHeader() that
contains the needed workarounds for UTF8 and IE.

Refactored download code to use the new API.

Removed unused trashbin download file.
Added workaround for Android content disposition

Fixes #5807
Fixing Issue #6301 on master branch
Added private var $certPath to store the user root cert

Move logic to determine the $certPath path to the constructor and modify to get the path from OC_User::getHome()

Add curl options to use the certificate to avoid certificate errors with self-signed certicates in the downdload/upload method so we don't get blank files
Fixing tab/space coding style
Only set SSL things when ```$this->secure``` is ```true```
Fix ```createCertificateBundle``` and  ```getCertificates``` methods
from ```OC_Mount_config``` to use ```OC_User::getHome``` to get the
path
fall back to getLocalFile if storage doesn't support fseek
fix the config option to remove the ability for users to set their displayname
Replace static usage of OC_Config and OC_Preferences with the injected \OC\ConfigAll
implement ftell stream wrapper and fix return value from fseek stream wrapper
spaces to tabs
extend the encryption stream wrapper to handle local files and add a fall back for file size calculation if the storage doesn't support fseek
test for isEncryptedPath()
add test for the stream wrapper to read encrypted files from the system folder /tmp
Removed numRows usage from encryption app

numRows on Oracle always seem to return 0.

This fix removes numRows usage from the encryption and sharing app.

This fixes unit tests and potentially the encryption app itself
(migration status) when running on Oracle
Merge branch 'master' into user-no-change-displayname