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
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
Enforce required phpunit version

This will prevent frustration and confusion when unit tests fail because
the wrong phpunit version was used
Added isUserAgent() method to request

- added isUserAgent() method to OC_Request which makes it possible to
  test it
- OC_Response::setContentDisposition now uses OC_Request::isUserAgent()
enable ldap tests
avoid conflict with physical file config.js
new config parameter 'front_controller_active' which will instruct the url generator to generate urls without index.php
use getAppWebPath() in here as well
reuse existing helper function OC_Helper::is_function_enabled
we shall explode on ',' only
trimming all array elements
Merge pull request #6290 from owncloud/files-androidcontentdisposition

Files androidcontentdisposition
Merge pull request #6660 from owncloud/fixing-disabled-function-checks

Fixing disabled function checks
Now also preventing to override "files" dir size with -1

Fixes #6526
Introduce user count action to user management
Add command line tool to show numbers of users and user directories
Merge pull request #6565 from owncloud/enable-ldap-unit-tests-master-2

enable ldap tests
Merge pull request #6594 from owncloud/kill-index.php-from-url

Kill index.php from url
[tx-robot] updated from transifex